text:
Lyrebird

A lyrebird is either of two species of ground-dwelling Australian birds that compose the genus Menura, and the family Menuridae. They are most notable for their impressive ability to mimic natural and artificial sounds from their environment, and the striking beauty of the male bird's huge tail when it is fanned out in courtship display. Lyrebirds have unique plumes of neutral-coloured tailfeathers and are among Australia's best-known native birds.

Taxonomy

The classification of lyrebirds was the subject of much debate after the first specimens reached European scientists after 1798. Based on specimens sent from New South Wales to England, Major-General Thomas Davies illustrated and described this species as the superb lyrebird, which he called Menura superba, in an 1800 presentation to the Linnean Society of London, but this work was not published until 1802; in the intervening time period, however, the species was described and named Menura novaehollandiae by John Latham in 1801, and this is the accepted name by virtue of nomenclatural priority.

The genus name Menura refers to the pattern of repeated transparent crescents (or "lunules") on the superb lyrebird's outer tail-feathers, from the Ancient Greek words μήνη mēnē "moon" and ουρά ourá "tail".

Lyrebirds are named because their outer tail feathers are broad and curved in a S shape that together resemble the shape of a lyre.

Systematics
Lyrebirds were thought to be Galliformes like the broadly similar looking partridge, junglefowl, and pheasants familiar to Europeans, reflected in the early names given to the superb lyrebird, including native pheasant. They were also called peacock-wrens and Australian birds-of-paradise. The idea that they were related to the pheasants was abandoned when the first chicks, which are altricial, were described. They were not classed with the passerines until a paper was published in 1840, twelve years after they were assigned a discrete family, Menuridae. Within that family they compose a single genus, Menura.

It is generally accepted that the lyrebird family is most closely related to the scrub-birds (Atrichornithidae) and some authorities combine both in a single family, but evidence that they are also related to the bowerbirds remains controversial.

Lyrebirds are ancient Australian animals: the Australian Museum has fossils of lyrebirds dating back to about 15 million years ago. The prehistoric Menura tyawanoides has been described from Early Miocene fossils found at the famous Riversleigh site.

Species
Two species of lyrebird are extant:

Description
The lyrebirds are large passerine birds, amongst the largest in the order. They are ground living birds with strong legs and feet and short rounded wings. They are poor fliers and rarely fly except for periods of downhill gliding. The superb lyrebird is the larger of the two species. Lyrebirds measure 31 to 39 inches in length, including their tail. Males tend to be slightly larger than females. Females weigh around 2 pounds, and males weigh around 2.4 pounds.

Distribution and habitat
The superb lyrebird is found in areas of rainforest in Victoria, New South Wales, and south-east Queensland. It is also found in Tasmania where it was introduced in the 19th century. Many superb lyrebirds live in the Dandenong Ranges National Park and Kinglake National Park around Melbourne, the Royal National Park and Illawarra region south of Sydney, in many other parks along the east coast of Australia, and non protected bushland. Albert's lyrebird is found only in a small area of Southern Queensland rainforest.

Behaviour and ecology
Lyrebirds are shy and difficult to approach, particularly the Albert's lyrebird, with the result that little information about its behaviour has been documented. When lyrebirds detect potential danger, they pause and scan the surroundings, sound an alarm, and either flee the area on foot, or seek cover and freeze. Firefighters sheltering in mine shafts during bushfires have been joined by lyrebirds.

Diet and feeding

Lyrebirds feed on the ground and as individuals. A range of invertebrate prey is taken, including insects such as cockroaches, beetles (both adults and larvae), earwigs, fly larvae, and the adults and larvae of moths. Other prey taken includes centipedes, spiders, earthworms. Less commonly taken prey includes stick insects, bugs, amphipods, lizards, frogs and occasionally, seeds. They find food by scratching with their feet through the leaf-litter.

Breeding

Lyrebirds are long-lived birds that can live as long as 30 years. They have long breeding cycles and start breeding later in life than other passerine birds. Female superb lyrebirds start breeding at the age of five or six, and males at the age of six to eight. Males defend territories from other males, and those territories may contain the breeding territories of up to eight females. Within the male territories, the males create or use display platforms; for the superb lyrebird, this is a mound of bare soil; for the Albert's lyrebird, it is a pile of twigs on the forest floor.

Male lyrebirds call mostly during winter, when they construct and maintain an open arena-mound in dense bush, on which they sing and dance in an elaborate courtship display performed for potential mates, of which the male lyrebird has several. The strength, volume, and location of the nest built by the female lyrebird is dependent on the rainfall and predation during the nest building period. It is important for the nest to be water resistant and hidden in secluded areas so predators cannot attack. Once the nest is made in the preferred location, the female lyrebird lays a single egg. The egg is incubated over 50 days solely by the female, and the female also fosters the chick alone.

Vocalizations and mimicry

A lyrebird's song is one of the more distinctive aspects of its behavioural biology. Lyrebirds sing throughout the year, but the peak of the breeding season, from June to August, is when they sing with the most intensity. During this peak males may sing for four hours of the day, almost half the hours of daylight. The song of the lyrebird is a mixture of elements of its own song and mimicry of other species. Lyrebirds render with great fidelity the individual songs of other birds and the chatter of flocks of birds, and also mimic other animals such as possums, koalas and dingoes. Lyrebirds have been recorded mimicking human sounds such as a mill whistle, a cross-cut saw, chainsaws, car engines and car alarms, fire alarms, rifle-shots, camera shutters, dogs barking, crying babies, music, mobile phone ring tones, and even the human voice. However, while the mimicry of human noises is widely reported, the extent to which it happens is exaggerated and the phenomenon is unusual. Parts of the lyrebird's own song can resemble human-made sound effects, which has given rise to the urban legend that they frequently imitate video game or film sounds.

The superb lyrebird's mimicked calls are learned from the local environment, including from other superb lyrebirds. An instructive example is the population of superb lyrebirds in Tasmania, which have retained the calls of species not native to Tasmania in their repertoire, with some local Tasmanian endemic bird songs added. The female lyrebirds of both species are also mimics capable of complex vocalisations. Superb lyrebird females are silent during courtship; however, they regularly produce sophisticated vocal displays during foraging and nest defense. A recording of a superb lyrebird mimicking sounds of an electronic shooting game, workmen and chainsaws was added to the National Film and Sound Archive's Sounds of Australia registry in 2013.

Both species of lyrebird produced elaborate lyrebird-specific vocalisations including 'whistle songs'. Males also sing songs specifically associated with their song and dance displays.

One researcher, Sydney Curtis, has recorded flute-like lyrebird calls in the vicinity of the New England National Park. Similarly, in 1969, a park ranger, Neville Fenton, recorded a lyrebird song which resembled flute sounds in the New England National Park, near Dorrigo in northern coastal New South Wales. After much detective work by Fenton, it was discovered that in the 1930s, a flute player living on a farm adjoining the park used to play tunes near his pet lyrebird. The lyrebird adopted the tunes into his repertoire, and retained them after release into the park. Neville Fenton forwarded a tape of his recording to Norman Robinson. Because a lyrebird is able to carry two tunes at the same time, Robinson filtered out one of the tunes and put it on the phonograph for the purposes of analysis. One witness suggested that the song represents a modified version of two popular tunes in the 1930s: "The Keel Row" and "Mosquito's Dance". Musicologist David Rothenberg has endorsed this information. However, a "flute lyrebird" research group (including Curtis and Fenton) formed to investigate the veracity of this story found no evidence of "Mosquito Dance" and only remnants of "Keel Row" in contemporary and historical lyrebird recordings from this area. Neither were they able to prove that a lyrebird chick had been a pet, although they acknowledged compelling evidence on both sides of the argument.

Status and conservation
Until the 2019–2020 Australian bushfire season, superb lyrebirds were not considered threatened in the short to medium term. Concern has since grown as early analyses have shown the extent of destruction of the lyrebird's preferred wet-forest habitats, which in less intense previous bushfire seasons have been spared, in large part due to their moisture content. Albert's lyrebird has a very restricted habitat and had been listed as vulnerable by the IUCN, but because the species and its habitat were carefully managed, the species was re-assessed to near threatened in 2009. The superb lyrebird had already been seriously threatened by habitat destruction in the past. Its population had since recovered, but the 2019–2020 bushfires damaged much of its habitat, which may lead to a reclassification of its status from "common" to "threatened". Beyond this new threat are the long-term vulnerabilities to predation by cats and foxes, as well as human population pressure on its habitat.

Painting by John Gould

The lyrebird is so called because the male bird has a spectacular tail, consisting of 16 highly modified feathers (two long slender lyrates at the centre of the plume, two broader medians on the outside edges and twelve filamentaries arrayed between them), which was originally thought to resemble a lyre. This happened when a superb lyrebird specimen (which had been taken from Australia to England during the early 19th century) was prepared for display at the British Museum by a taxidermist who had never seen a live lyrebird. The taxidermist mistakenly thought that the tail would resemble a lyre, and that the tail would be held in a similar way to that of a peacock during courtship display, and so he arranged the feathers in this way. Later, John Gould (who had also never seen a live lyrebird), painted the lyrebird from the British Museum specimen.

The male lyrebird's tail is not held as in John Gould's painting. Instead, the male lyrebird's tail is fanned over the lyrebird during courtship display, with the tail completely covering his head and back—as can be seen in the image in the "breeding" section of this page, and also the image of the 10-cent coin, where the superb lyrebird's tail (in courtship display) is portrayed accurately.

Lyrebird emblems and logos

The lyrebird has been featured as a symbol and emblem many times, especially in New South Wales and Victoria (where the superb lyrebird has its natural habitat), and in Queensland (where Albert's lyrebird has its natural habitat).

 * A male superb lyrebird is featured on the reverse of the Australian 10-cent coin.
 * A superb lyrebird featured on the Australian one shilling postage stamp first issued in 1932.
 * A stylised superb lyrebird appears in the transparent window of the Australian 100 dollar note.
 * A silhouette of a male superb lyrebird is the logo of the Australian Film Commission.
 * An illustration of a male superb lyrebird, in courtship display, is the emblem of the New South Wales National Parks and Wildlife Service.
 * The pattern on the curtains of the Victorian State Theatre is the image of a male superb lyrebird, in courtship display, as viewed from the front.
 * A stylised illustration of a male Albert's lyrebird was the logo of the Queensland Conservatorium of Music, before the Conservatorium became part of Griffith University. In the logo, the top part of the lyrebird's tail became a music stave.
 * Australian band You Am I's 2008 album Dilettantes and its first single, "Erasmus", feature a drawing of a lyrebird by artist Ken Taylor.
 * A stylised illustration of part of a male superb lyrebird's tail is the logo for the Lyrebird Arts Council of Victoria.
 * The lyrebird is also featured atop the crest of Panhellenic Sorority Alpha Chi Omega, whose symbol is the lyre.
 * There are many other companies with the name of Lyrebird, and these also have lyrebird logos.
 * "Land of the Lyrebird" is an alternative name for the Strzelecki Ranges in the Gippsland region of Victoria.
 * A silhouetted male superb lyrebird in courtship display features in the masthead of The Betoota Advocate.

Further references

 * Attenborough, D. (1998). The Life of Birds. p. 212. ISBN 0563-38792-0.

title: Lyrebird


text:
Simulation language

A computer simulation language is used to describe the operation of a simulation on a computer. There are two major types of simulation: continuous and discrete event though more modern languages can handle more complex combinations. Most languages also have a graphical interface and at least a simple statistic gathering capability for the analysis of the results. An important part of discrete-event languages is the ability to generate pseudo-random numbers and variants from different probability distributions.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

title: Simulation language


text:
Atomic radius

The atomic radius of a chemical element is a measure of the size of its atom, usually the mean or typical distance from the center of the nucleus to the outermost isolated electron. Since the boundary is not a well-defined physical entity, there are various non-equivalent definitions of atomic radius. Four widely used definitions of atomic radius are: Van der Waals radius, ionic radius, metallic radius  and covalent radius. Typically, because of the difficulty to isolate atoms in order to measure their radii separately, atomic radius is measured in a chemically bonded state; however theoretical calculations are simpler when considering atoms in isolation. The dependencies on environment, probe, and state lead to a multiplicity of definitions.

Depending on the definition, the term may apply to atoms in condensed matter, covalently bonding in molecules, or in ionized and excited states; and its value may be obtained through experimental measurements, or computed from theoretical models. The value of the radius may depend on the atom's state and context.

Electrons do not have definite orbits nor sharply defined ranges. Rather, their positions must be described as probability distributions that taper off gradually as one moves away from the nucleus, without a sharp cutoff; these are referred to as atomic orbitals or electron clouds. Moreover, in condensed matter and molecules, the electron clouds of the atoms usually overlap to some extent, and some of the electrons may roam over a large region encompassing two or more atoms.

Under most definitions the radii of isolated neutral atoms range between 30 and 300 pm (trillionths of a meter), or between 0.3 and 3 ångströms. Therefore, the radius of an atom is more than 10,000 times the radius of its nucleus (1–10 fm), and less than 1/1000 of the wavelength of visible light (400–700 nm).

For many purposes, atoms can be modeled as spheres. This is only a crude approximation, but it can provide quantitative explanations and predictions for many phenomena, such as the density of liquids and solids, the diffusion of fluids through molecular sieves, the arrangement of atoms and ions in crystals, and the size and shape of molecules.

History
In 1920, shortly after it had become possible to determine the sizes of atoms using X-ray crystallography, it was suggested that all atoms of the same element have the same radii. However, in 1923, when more crystal data had become available, it was found that the approximation of an atom as a sphere does not necessarily hold when comparing the same atom in different crystal structures.

Definitions
Widely used definitions of atomic radius include:

 * Van der Waals radius: In the simplest definition, half the minimum distance between the nuclei of two atoms of the element that are not otherwise bound by covalent or metallic interactions. The Van der Waals radius may be defined even for elements (such as metals) in which Van der Waals forces are dominated by other interactions.  Because Van der Waals interactions arise through quantum fluctuations of the atomic polarisation, the polarisability (which can usually be measured or calculated more easily) may be used to define the Van der Waals radius indirectly.

 * Ionic radius: the nominal radius of the ions of an element in a specific ionization state, deduced from the spacing of atomic nuclei in crystalline salts that include that ion. In principle, the spacing between two adjacent oppositely charged ions (the length of the ionic bond between them) should equal the sum of their ionic radii.
 * Covalent radius: the nominal radius of the atoms of an element when covalently bound to other atoms, as deduced from the separation between the atomic nuclei in molecules. In principle, the distance between two atoms that are bound to each other in a molecule (the length of that covalent bond) should equal the sum of their covalent radii.
 * Metallic radius: the nominal radius of atoms of an element when joined to other atoms by metallic bonds.
 * Bohr radius: the radius of the lowest-energy electron orbit predicted by Bohr model of the atom (1913).  It is only applicable to atoms and ions with a single electron, such as hydrogen, singly ionized helium, and positronium.  Although the model itself is now obsolete, the Bohr radius for the hydrogen atom is still regarded as an important physical constant, because it is equivalent to the quantum-mechanical most probable distance of the electron from the nucleus.

Empirically measured atomic radius
The following table shows empirically measured covalent radii for the elements, as published by J. C. Slater in 1964. The values are in picometers (pm or 1×10−12 m), with an accuracy of about 5 pm. The shade of the box ranges from red to yellow as the radius increases; gray indicates lack of data.

Explanation of the general trends
The way the atomic radius varies with increasing atomic number can be explained by the arrangement of electrons in shells of fixed capacity. The shells are generally filled in order of increasing radius, since the negatively charged electrons are attracted by the positively charged protons in the nucleus. As the atomic number increases along each row of the periodic table, the additional electrons go into the same outermost shell; whose radius gradually contracts, due to the increasing nuclear charge. In a noble gas, the outermost shell is completely filled; therefore, the additional electron of next alkali metal will go into the next outer shell, accounting for the sudden increase in the atomic radius.

The increasing nuclear charge is partly counterbalanced by the increasing number of electrons, a phenomenon that is known as shielding; which explains why the size of atoms usually increases down each column. However, there is one notable exception, known as the lanthanide contraction: the 5d block of elements are much smaller than one would expect, due to the weak shielding of the 4f electrons.

Essentially, the atomic radius decreases across the periods due to an increasing number of protons. Therefore, there is a greater attraction between the protons and electrons because opposite charges attract, and more protons create a stronger charge. The greater attraction draws the electrons closer to the protons, decreasing the size of the particle. Therefore, the atomic radius decreases. Down the groups, atomic radius increases. This is because there are more energy levels and therefore a greater distance between protons and electrons. In addition, electron shielding causes attraction to decrease, so remaining electrons can go farther away from the positively charged nucleus. Therefore, the size, or atomic radius, increases.

The following table summarizes the main phenomena that influence the atomic radius of an element:

Lanthanide contraction
The electrons in the 4f-subshell, which is progressively filled from lanthanum (Z = 57) to ytterbium (Z = 70), are not particularly effective at shielding the increasing nuclear charge from the sub-shells further out. The elements immediately following the lanthanides have atomic radii which are smaller than would be expected and which are almost identical to the atomic radii of the elements immediately above them. Hence lutetium is in fact slightly smaller than yttrium, hafnium has virtually the same atomic radius (and chemistry) as zirconium, and tantalum has an atomic radius similar to niobium, and so forth. The effect of the lanthanide contraction is noticeable up to platinum (Z = 78), after which it is masked by a relativistic effect known as the inert-pair effect.

Due to lanthanide contraction, the 5 following observations can be drawn:

La3+ > Ce3+ > ..., ... > Lu3+.
 * 1) The size of Ln3+ ions regularly decreases with atomic number. According to Fajans' rules, decrease in size of Ln3+ ions increases the covalent character and decreases the basic character between Ln3+ and  OH− ions in Ln(OH)3, to the point that Yb(OH)3 and Lu(OH)3 can dissolve with difficulty in hot concentrated NaOH. Hence the order of size of Ln3+ is given:
 * 1) There is a regular decrease in their ionic radii.
 * 2) There is a regular decrease in their tendency to act as a reducing agent, with an increase in atomic number.
 * 3) The second and third rows of d-block transition elements are quite close in properties.
 * 4) Consequently, these elements occur together in natural minerals and are difficult to separate.

d-block contraction
The d-block contraction is less pronounced than the lanthanide contraction but arises from a similar cause. In this case, it is the poor shielding capacity of the 3d-electrons which affects the atomic radii and chemistries of the elements immediately following the first row of the transition metals, from gallium (Z = 31) to bromine (Z = 35).

Calculated atomic radius
The following table shows atomic radii computed from theoretical models, as published by Enrico Clementi and others in 1967. The values are in picometres (pm).

title: Atomic radius


text:
Kilogram per cubic metre

The kilogram per cubic metre (symbol: kg·m−3, or kg/m3) is the unit of density in the International System of Units (SI). It is defined by dividing the SI unit of mass, the kilogram, by the SI unit of volume, the cubic metre.

Conversions

 * 1 kg/m3 = 1 g/L (exactly)
 * 1 kg/m3 = 0.001 g/cm3 (exactly)
 * 1 kg/m3 ≈ 0.06243 lb/ft3 (approximately)
 * 1 kg/m3 ≈ 0.1335 oz/US gal (approximately)
 * 1 kg/m3 ≈ 0.1604 oz/imp gal (approximately)

 * 1 g/cm3 = 1000 kg/m3 (exactly)
 * 1 lb/ft3 ≈ 16.02 kg/m3 (approximately)
 * 1 oz/(US gal) ≈ 7.489 kg/m3 (approximately)
 * 1 oz/(imp gal) ≈ 6.236 kg/m3 (approximately)

Relation to other measures
The density of water is about 1000 kg/m3 or 1 g/cm3, because the size of the gram was originally based on the mass of a cubic centimetre of water.

In chemistry, g/cm3 is more commonly used.

title: Kilogram per cubic metre


text:
Nucleosynthesis

Nucleosynthesis is the process that creates new atomic nuclei from pre-existing nucleons (protons and neutrons) and nuclei. According to current theories, the first nuclei were formed a few minutes after the Big Bang, through nuclear reactions in a process called Big Bang nucleosynthesis. After about 20 minutes, the universe had expanded and cooled to a point at which these high-energy collisions among nucleons ended, so only the fastest and simplest reactions occurred, leaving our universe containing hydrogen and helium. The rest is traces of other elements such as lithium and the hydrogen isotope deuterium. Nucleosynthesis in stars and their explosions later produced the variety of elements and isotopes that we have today, in a process called cosmic chemical evolution. The amounts of total mass in elements heavier than hydrogen and helium (called 'metals' by astrophysicists) remains small (few percent), so that the universe still has approximately the same composition.

Stars fuse light elements to heavier ones in their cores, giving off energy in the process known as stellar nucleosynthesis. Nuclear fusion reactions create many of the lighter elements, up to and including iron and nickel in the most massive stars. Products of stellar nucleosynthesis remain trapped in stellar cores and remnants except if ejected through stellar winds and explosions. The neutron capture reactions of the r-process and s-process create heavier elements, from iron upwards.

Supernova nucleosynthesis within exploding stars is largely responsible for the elements between oxygen and rubidium: from the ejection of elements produced during stellar nucleosynthesis; through explosive nucleosynthesis during the supernova explosion; and from the r-process (absorption of multiple neutrons) during the explosion.

Neutron star mergers are a recently discovered major source of elements produced in the r-process. When two neutron stars collide, a significant amount of neutron-rich matter may be ejected which then quickly forms heavy elements.

Cosmic ray spallation is a process wherein cosmic rays impact nuclei and fragment them. It is a significant source of the lighter nuclei, particularly 3He, 9Be and 10,11B, that are not created by stellar nucleosynthesis. Cosmic ray spallation can occur in the interstellar medium, on asteroids and meteoroids, or on Earth in the atmosphere or in the ground. This contributes to the presence on Earth of cosmogenic nuclides.

On Earth new nuclei are also produced by radiogenesis, the decay of long-lived, primordial radionuclides such as uranium, thorium, and potassium-40.

Timeline
It is thought that the primordial nucleons themselves were formed from the quark–gluon plasma around 13.8 billion years ago during the Big Bang as it cooled below two trillion degrees. A few minutes afterwards, starting with only protons and neutrons, nuclei up to lithium and beryllium (both with mass number 7) were formed, but hardly any other elements. Some boron may have been formed at this time, but the process stopped before significant carbon could be formed, as this element requires a far higher product of helium density and time than were present in the short nucleosynthesis period of the Big Bang. That fusion process essentially shut down at about 20 minutes, due to drops in temperature and density as the universe continued to expand. This first process, Big Bang nucleosynthesis, was the first type of nucleogenesis to occur in the universe, creating the so-called primordial elements.

A star formed in the early universe produces heavier elements by combining its lighter nuclei – hydrogen, helium, lithium, beryllium, and boron – which were found in the initial composition of the interstellar medium and hence the star. Interstellar gas therefore contains declining abundances of these light elements, which are present only by virtue of their nucleosynthesis during the Big Bang, and also cosmic ray spallation. These lighter elements in the present universe are therefore thought to have been produced through thousands of millions of years of cosmic ray (mostly high-energy proton) mediated breakup of heavier elements in interstellar gas and dust. The fragments of these cosmic-ray collisions include helium-3 and the stable isotopes of the light elements lithium, beryllium, and boron. Carbon was not made in the Big Bang, but was produced later in larger stars via the triple-alpha process.

The subsequent nucleosynthesis of heavier elements (Z ≥ 6, carbon and heavier elements) requires the extreme temperatures and pressures found within stars and supernovae. These processes began as hydrogen and helium from the Big Bang collapsed into the first stars after about 500 million years. Star formation has been occurring continuously in galaxies since that time. The primordial nuclides were created by Big Bang nucleosynthesis, stellar nucleosynthesis, supernova nucleosynthesis, and by nucleosynthesis in exotic events such as neutron star collisions. Other nuclides, such as $40$Ar, formed later through radioactive decay. On Earth, mixing and evaporation has altered the primordial composition to what is called the natural terrestrial composition. The heavier elements produced after the Big Bang range in atomic numbers from Z = 6 (carbon) to Z = 94 (plutonium). Synthesis of these elements occurred through nuclear reactions involving the strong and weak interactions among nuclei, and called nuclear fusion (including both rapid and slow multiple neutron capture), and include also nuclear fission and radioactive decays such as beta decay. The stability of atomic nuclei of different sizes and composition (i.e. numbers of neutrons and protons) plays an important role in the possible reactions among nuclei. Cosmic nucleosynthesis, therefore, is studied among researchers of astrophysics and nuclear physics ("nuclear astrophysics").

History of nucleosynthesis theory
The first ideas on nucleosynthesis were simply that the chemical elements were created at the beginning of the universe, but no rational physical scenario for this could be identified. Gradually it became clear that hydrogen and helium are much more abundant than any of the other elements. All the rest constitute less than 2% of the mass of the Solar System, and of other star systems as well. At the same time it was clear that oxygen and carbon were the next two most common elements, and also that there was a general trend toward high abundance of the light elements, especially those with isotopes composed of whole numbers of helium-4 nuclei (alpha nuclides).

Arthur Stanley Eddington first suggested in 1920, that stars obtain their energy by fusing hydrogen into helium and raised the possibility that the heavier elements may also form in stars. This idea was not generally accepted, as the nuclear mechanism was not understood. In the years immediately before World War II, Hans Bethe first elucidated those nuclear mechanisms by which hydrogen is fused into helium.

Fred Hoyle's original work on nucleosynthesis of heavier elements in stars, occurred just after World War II. His work explained the production of all heavier elements, starting from hydrogen. Hoyle proposed that hydrogen is continuously created in the universe from vacuum and energy, without need for universal beginning.

Hoyle's work explained how the abundances of the elements increased with time as the galaxy aged. Subsequently, Hoyle's picture was expanded during the 1960s by contributions from William A. Fowler, Alastair G. W. Cameron, and Donald D. Clayton, followed by many others. The seminal 1957 review paper by E. M. Burbidge, G. R. Burbidge, Fowler and Hoyle is a well-known summary of the state of the field in 1957. That paper defined new processes for the transformation of one heavy nucleus into others within stars, processes that could be documented by astronomers.

The Big Bang itself had been proposed in 1931, long before this period, by Georges Lemaître, a Belgian physicist, who suggested that the evident expansion of the Universe in time required that the Universe, if contracted backwards in time, would continue to do so until it could contract no further. This would bring all the mass of the Universe to a single point, a "primeval atom", to a state before which time and space did not exist. Hoyle is credited with coining the term "Big Bang" during a 1949 BBC radio broadcast, saying that Lemaître's theory was "based on the hypothesis that all the matter in the universe was created in one big bang at a particular time in the remote past." It is popularly reported that Hoyle intended this to be pejorative, but Hoyle explicitly denied this and said it was just a striking image meant to highlight the difference between the two models. Lemaître's model was needed to explain the existence of deuterium and nuclides between helium and carbon, as well as the fundamentally high amount of helium present, not only in stars but also in interstellar space. As it happened, both Lemaître and Hoyle's models of nucleosynthesis would be needed to explain the elemental abundances in the universe.

The goal of the theory of nucleosynthesis is to explain the vastly differing abundances of the chemical elements and their several isotopes from the perspective of natural processes. The primary stimulus to the development of this theory was the shape of a plot of the abundances versus the atomic number of the elements. Those abundances, when plotted on a graph as a function of atomic number, have a jagged sawtooth structure that varies by factors up to ten million. A very influential stimulus to nucleosynthesis research was an abundance table created by Hans Suess and Harold Urey that was based on the unfractionated abundances of the non-volatile elements found within unevolved meteorites. Such a graph of the abundances is displayed on a logarithmic scale below, where the dramatically jagged structure is visually suppressed by the many powers of ten spanned in the vertical scale of this graph.

Processes
There are a number of astrophysical processes which are believed to be responsible for nucleosynthesis. The majority of these occur within stars, and the chain of those nuclear fusion processes are known as hydrogen burning (via the proton–proton chain or the CNO cycle), helium burning, carbon burning, neon burning, oxygen burning and silicon burning. These processes are able to create elements up to and including iron and nickel. This is the region of nucleosynthesis within which the isotopes with the highest binding energy per nucleon are created. Heavier elements can be assembled within stars by a neutron capture process known as the s-process or in explosive environments, such as supernovae and neutron star mergers, by a number of other processes. Some of those others include the r-process, which involves rapid neutron captures, the rp-process, and the p-process (sometimes known as the gamma process), which results in the photodisintegration of existing nuclei.

Big Bang nucleosynthesis
Big Bang nucleosynthesis occurred within the first three minutes of the beginning of the universe and is responsible for much of the abundance of (protium),  (D, deuterium),  (helium-3), and  (helium-4). Although continues to be produced by stellar fusion and alpha decays and trace amounts of  continue to be produced by spallation and certain types of radioactive decay, most of the mass of the isotopes in the universe are thought to have been produced in the Big Bang. The nuclei of these elements, along with some and  are considered to have been formed between 100 and 300 seconds after the Big Bang when the primordial quark–gluon plasma froze out to form protons and neutrons. Because of the very short period in which nucleosynthesis occurred before it was stopped by expansion and cooling (about 20 minutes), no elements heavier than beryllium (or possibly boron) could be formed. Elements formed during this time were in the plasma state, and did not cool to the state of neutral atoms until much later.

Stellar nucleosynthesis
Stellar nucleosynthesis is the nuclear process by which new nuclei are produced. It occurs in stars during stellar evolution. It is responsible for the galactic abundances of elements from carbon to iron. Stars are thermonuclear furnaces in which H and He are fused into heavier nuclei by increasingly high temperatures as the composition of the core evolves. Of particular importance is carbon because its formation from He is a bottleneck in the entire process. Carbon is produced by the triple-alpha process in all stars. Carbon is also the main element that causes the release of free neutrons within stars, giving rise to the s-process, in which the slow absorption of neutrons converts iron into elements heavier than iron and nickel.

The products of stellar nucleosynthesis are generally dispersed into the interstellar gas through mass loss episodes and the stellar winds of low mass stars. The mass loss events can be witnessed today in the planetary nebulae phase of low-mass star evolution, and the explosive ending of stars, called supernovae, of those with more than eight times the mass of the Sun.

The first direct proof that nucleosynthesis occurs in stars was the astronomical observation that interstellar gas has become enriched with heavy elements as time passed. As a result, stars that were born from it late in the galaxy, formed with much higher initial heavy element abundances than those that had formed earlier. The detection of technetium in the atmosphere of a red giant star in 1952, by spectroscopy, provided the first evidence of nuclear activity within stars. Because technetium is radioactive, with a half-life much less than the age of the star, its abundance must reflect its recent creation within that star. Equally convincing evidence of the stellar origin of heavy elements is the large overabundances of specific stable elements found in stellar atmospheres of asymptotic giant branch stars. Observation of barium abundances some 20–50 times greater than found in unevolved stars is evidence of the operation of the s-process within such stars. Many modern proofs of stellar nucleosynthesis are provided by the isotopic compositions of stardust, solid grains that have condensed from the gases of individual stars and which have been extracted from meteorites. Stardust is one component of cosmic dust and is frequently called presolar grains. The measured isotopic compositions in stardust grains demonstrate many aspects of nucleosynthesis within the stars from which the grains condensed during the star's late-life mass-loss episodes.

Explosive nucleosynthesis
Supernova nucleosynthesis occurs in the energetic environment in supernovae, in which the elements between silicon and nickel are synthesized in quasiequilibrium established during fast fusion that attaches by reciprocating balanced nuclear reactions to 28Si. Quasiequilibrium can be thought of as almost equilibrium except for a high abundance of the 28Si nuclei in the feverishly burning mix. This concept was the most important discovery in nucleosynthesis theory of the intermediate-mass elements since Hoyle's 1954 paper because it provided an overarching understanding of the abundant and chemically important elements between silicon (A = 28) and nickel (A = 60). It replaced the incorrect although much cited alpha process of the B2FH paper, which inadvertently obscured Hoyle's 1954 theory. Further nucleosynthesis processes can occur, in particular the r-process (rapid process) described by the B2FH paper and first calculated by Seeger, Fowler and Clayton, in which the most neutron-rich isotopes of elements heavier than nickel are produced by rapid absorption of free neutrons. The creation of free neutrons by electron capture during the rapid compression of the supernova core along with the assembly of some neutron-rich seed nuclei makes the r-process a primary process, and one that can occur even in a star of pure H and He. This is in contrast to the B2FH designation of the process as a secondary process. This promising scenario, though generally supported by supernova experts, has yet to achieve a satisfactory calculation of r-process abundances. The primary r-process has been confirmed by astronomers who had observed old stars born when galactic metallicity was still small, that nonetheless contain their complement of r-process nuclei; thereby demonstrating that the metallicity is a product of an internal process. The r-process is responsible for our natural cohort of radioactive elements, such as uranium and thorium, as well as the most neutron-rich isotopes of each heavy element.

The rp-process (rapid proton) involves the rapid absorption of free protons as well as neutrons, but its role and its existence are less certain.

Explosive nucleosynthesis occurs too rapidly for radioactive decay to decrease the number of neutrons, so that many abundant isotopes with equal and even numbers of protons and neutrons are synthesized by the silicon quasi-equilibrium process. During this process, the burning of oxygen and silicon fuses nuclei that themselves have equal numbers of protons and neutrons to produce nuclides which consist of whole numbers of helium nuclei, up to 15 (representing 60Ni). Such multiple-alpha-particle nuclides are totally stable up to 40Ca (made of 10 helium nuclei), but heavier nuclei with equal and even numbers of protons and neutrons are tightly bound but unstable. The quasi-equilibrium produces radioactive isobars 44Ti, 48Cr, 52Fe, and 56Ni, which (except 44Ti) are created in abundance but decay after the explosion and leave the most stable isotope of the corresponding element at the same atomic weight. The most abundant and extant isotopes of elements produced in this way are 48Ti, 52Cr, and 56Fe. These decays are accompanied by the emission of gamma-rays (radiation from the nucleus), whose spectroscopic lines can be used to identify the isotope created by the decay. The detection of these emission lines were an important early product of gamma-ray astronomy.

The most convincing proof of explosive nucleosynthesis in supernovae occurred in 1987 when those gamma-ray lines were detected emerging from supernova 1987A. Gamma-ray lines identifying 56Co and 57Co nuclei, whose half-lives limit their age to about a year, proved that their radioactive cobalt parents created them. This nuclear astronomy observation was predicted in 1969 as a way to confirm explosive nucleosynthesis of the elements, and that prediction played an important role in the planning for NASA's Compton Gamma-Ray Observatory.

Other proofs of explosive nucleosynthesis are found within the stardust grains that condensed within the interiors of supernovae as they expanded and cooled. Stardust grains are one component of cosmic dust. In particular, radioactive 44Ti was measured to be very abundant within supernova stardust grains at the time they condensed during the supernova expansion. This confirmed a 1975 prediction of the identification of supernova stardust (SUNOCONs), which became part of the pantheon of presolar grains. Other unusual isotopic ratios within these grains reveal many specific aspects of explosive nucleosynthesis.

Neutron star mergers
The merger of binary neutron stars (BNSs) is now believed to be the main source of r-process elements. Being neutron-rich by definition, mergers of this type had been suspected of being a source of such elements, but definitive evidence was difficult to obtain. In 2017 strong evidence emerged, when LIGO, VIRGO, the Fermi Gamma-ray Space Telescope and INTEGRAL, along with a collaboration of many observatories around the world, detected both gravitational wave and electromagnetic signatures of a likely neutron star merger, GW170817, and subsequently detected signals of numerous heavy elements such as gold as the ejected degenerate matter decays and cools. The first detection of the merger of a neutron star and black hole (NSBHs) came in July 2021 and more after but analysis seem to favor BNSs over NSBHs as the main contributors to heavy metal production.

Black hole accretion disk nucleosynthesis
Nucleosynthesis may happen in accretion disks of black holes.

Cosmic ray spallation
Cosmic ray spallation process reduces the atomic weight of interstellar matter by the impact with cosmic rays, to produce some of the lightest elements present in the universe (though not a significant amount of deuterium). Most notably spallation is believed to be responsible for the generation of almost all of 3He and the elements lithium, beryllium, and boron, although some 7Lithium and 7Beryllium are thought to have been produced in the Big Bang. The spallation process results from the impact of cosmic rays (mostly fast protons) against the interstellar medium. These impacts fragment carbon, nitrogen, and oxygen nuclei present. The process results in the light elements beryllium, boron, and lithium in the cosmos at much greater abundances than they are found within solar atmospheres. The quantities of the light elements 1H and 4He produced by spallation are negligible relative to their primordial abundance.

Beryllium and boron are not significantly produced by stellar fusion processes, since 8Be has an extremely short half-life of $8.2$ seconds.

Empirical evidence
Theories of nucleosynthesis are tested by calculating isotope abundances and comparing those results with observed abundances. Isotope abundances are typically calculated from the transition rates between isotopes in a network. Often these calculations can be simplified as a few key reactions control the rate of other reactions.

Minor mechanisms and processes
Tiny amounts of certain nuclides are produced on Earth by artificial means. Those are our primary source, for example, of technetium. However, some nuclides are also produced by a number of natural means that have continued after primordial elements were in place. These often act to create new elements in ways that can be used to date rocks or to trace the source of geological processes. Although these processes do not produce the nuclides in abundance, they are assumed to be the entire source of the existing natural supply of those nuclides.

These mechanisms include:
 * Radioactive decay may lead to radiogenic daughter nuclides. The nuclear decay of many long-lived primordial isotopes, especially uranium-235, uranium-238, and thorium-232 produce many intermediate daughter nuclides before they too finally decay to isotopes of lead. The Earth's natural supply of elements like radon and polonium is via this mechanism. The atmosphere's supply of argon-40 is due mostly to the radioactive decay of potassium-40 in the time since the formation of the Earth. Little of the atmospheric argon is primordial. Helium-4 is produced by alpha-decay, and the helium trapped in Earth's crust is also mostly non-primordial. In other types of radioactive decay, such as cluster decay, larger species of nuclei are ejected (for example, neon-20), and these eventually become newly formed stable atoms.
 * Radioactive decay may lead to spontaneous fission. This is not cluster decay, as the fission products may be split among nearly any type of atom. Thorium-232, uranium-235, and uranium-238 are primordial isotopes that undergo spontaneous fission. Natural technetium and promethium are produced in this manner.
 * Nuclear reactions. Naturally occurring nuclear reactions powered by radioactive decay give rise to so-called nucleogenic nuclides. This process happens when an energetic particle from radioactive decay, often an alpha particle, reacts with a nucleus of another atom to change the nucleus into another nuclide. This process may also cause the production of further subatomic particles, such as neutrons. Neutrons can also be produced in spontaneous fission and by neutron emission. These neutrons can then go on to produce other nuclides via neutron-induced fission, or by neutron capture. For example, some stable isotopes such as neon-21 and neon-22 are produced by several routes of nucleogenic synthesis, and thus only part of their abundance is primordial.
 * Nuclear reactions due to cosmic rays. By convention, these reaction-products are not termed "nucleogenic" nuclides, but rather cosmogenic nuclides. Cosmic rays continue to produce new elements on Earth by the same cosmogenic processes discussed above that produce primordial beryllium and boron. One important example is carbon-14, produced from nitrogen-14 in the atmosphere by cosmic rays. Iodine-129 is another example.

title: Nucleosynthesis


text:
Talk:List of Slovenian mathematicians

Untitled
This is interesting, but unless there is some unifying history or reason to distinguish mathematicians by nationality as opposed to their philosophy of mathematics, there doesn't seem to be much validity to this separate list.

title: Talk:List of Slovenian mathematicians


text:
People's Bank of China

The People's Bank of China (officially PBC and unofficially PBOC ) is the central bank of the People's Republic of China. It is responsible for carrying out monetary policy as determined by the People's Bank Law and the Commercial Bank Law.

The PBC was established in 1948 and became China's sole central bank after the founding of the People's Republic of China in 1949. From 1969 to 1978, the PBC was demoted to a bureau of the Ministry of Finance. The PBC was extensively reformed during the 1990s, when its provincial and local branches were abolished, instead opening nine regional branches. In 2023, these reforms were reversed as when the regional branches were abolished and the provincial branches restored, and new arrangements essentially ended the PBC's longstanding role in financial supervision.

The PBC is the 25th-ranked of 26 ministerial-level departments of the State Council, right ahead of the National Audit Office. The PBC lacks central bank independence, and is required to implement the policies of the Chinese Communist Party (CCP) under the direction of the party's Central Financial Commission. The PBC is led by a Governor assisted by several Deputy Governors and a CCP Committee Secretary. Since 2023, the roles of Governor and CCP Committee Secretary have been held jointly by Pan Gongsheng.

Mao era
The bank was established on December 1, 1948, based on the consolidation of the Huabei Bank, the Beihai Bank and Northwestern Farmers' Bank. The headquarters was first located in Shijiazhuang, Hebei, and then moved to Beijing in 1949. Between 1950 and 1978 the PBC was the only bank in the People's Republic of China and was responsible for both central banking and commercial banking operations. All other banks within mainland China such as the Bank of China were either organized as divisions of the PBC or were non-deposit taking agencies.

From 1952 to 1955 government shares were added to private banks to make state-private banks, until under the first Five Year plan from 1955 to 1959 the PBC had complete control of the private banks, making them branches of the PBC, closely resembling the vision of Vladimir Lenin. With aid from the Soviet Union, the shares of private enterprises and with them industrial output followed a similar path, forming a Soviet-style planned economy.

During the Cultural Revolution, the PBC suspended its commercial banking service. In June 1969, the State Council approved the consolidation of PBC's headquarters as a bureau within the Ministry of Finance. In that context, the PBC's head office was downsized to no more than eighty staff. Local PBC branches were correspondingly merged into local government finance departments.

Early reform era
The institutional demotion of the PBC was reversed in March 1978 as it was separated from the Finance Ministry and granted ministerial ranking.

By then and with the exception of special allocations for rural development, the monolithic PBC dominated all business transactions and credit. In 1979, China initiated a transition from that single-tier banking system to a two-tier system, which was largely completed by 1984. In March 1979, as part of the Chinese economic reforms, the State Council split off state-owned banks from the PBC, first the Agricultural Bank of China (ABC) and the Bank of China (BOC). The People's Construction Bank of China, which had been run separately under the Ministry of Finance, was also made autonomous (and later renamed China Construction Bank in 1986). In January 1984, the PBC's own commercial banking operations were spun off as the Industrial and Commercial Bank of China (ICBC). In September 1983, the State Council had promulgated that the PBC would function exclusively as the central bank of China and no longer undertake commercial banking activities.

Modernization efforts continued in the late 1980s and early 1990s. In 1990, the PBC moved into its new head office building, prominently located on West Chang'an Avenue. In 1991, vice governor Chen Yuan spearheaded the creation of the Electronic Interbank System (EIS), the PBC's first state-of-the-art financial market infrastructure. In 1992, however, the PBC had to reluctantly concede the spinning off of its securities regulatory duties to the newly established China Securities Regulatory Commission, whose first chair was former PBC vice governor Liu Hongru.

The bank's profile was greatly raised by the appointment of Zhu Rongji as its Governor in 1993, simultaneously as his role as Vice Premier in charge of economic and financial affairs.. Its central bank status was legally confirmed on March 18, 1995, by the 3rd Plenum of the 8th National People's Congress, and was granted a higher degree of autonomy than other State Council ministries by an act that year. In 1996 and 1996, the PBC established fundamental regulations on loans and consumer credit.

In 1998, the PBC underwent a major restructuring. All provincial and local branches were abolished, and the PBC opened nine regional branches, whose boundaries did not correspond to local administrative boundaries. The nine branches were located in Chengdu, Guangzhou, Jinan, Nanjing, Shanghai, Shenyang, Tianjin, Wuhan, and Xi'an, complemented by a sub-provincial network of city-level and county-level sub-branches. That same year, the so-called credit plan, a key feature of China's former state planning process, was finally abandoned, allowing the PBC to play a genuine role as monetary policy authority.

21st century
In 2003, the Standing Committee of the National People's Congress approved an amendment law for strengthening the role of PBC in the making and implementation of monetary policy for safeguarding the overall financial stability and provision of financial services. That year, the long overdue restructuring of China's banking sector made major progress with the creation of Central Huijin Investment, a PBC-managed fund that allowed the PBC to take the lead from the Ministry of Finance on the restructuring process and from the CCP Central Organization Department on the appointment of senior bank executives. That same year, however, the PBC reluctantly lost its direct authority over banking supervision with the creation of the China Banking Regulatory Commission.

In 2005, the PBC elevated its branch in Shanghai to the status of "second head office", in a move intended to mirror the prominent market-facing role of the Federal Reserve Bank of New York within the US Federal Reserve System. In 2006, the PBC established the Credit Reference Centre to provide financial credit reporting. In 2008, the PBC lost the direct ownership stakes it had built up in much of China's financial sector as the ownership of Central Huijin was transferred to the China Investment Corporation (CIC), a newly created sovereign wealth fund.

During the Great Recession, the PBC helped address bank liquidity crisis by signing swap agreements with numerous other countries to provide them with liquidity based on the renminbi. , China has swap agreements with 40 countries.

In 2010, the PBC issued administrative measures regarding online non-financial payment services. These measures retroactively recognized the legal status of online third-party payment platforms like Alipay. Prior to the 2010 measures, these services existed in a legal grey area.

In 2015, the PBC hosted China's first formal deposit insurance scheme. In 2019, this scheme was reorganized as a subsidiary of the PBC, the Deposit Insurance Fund Management Company. Meanwhile, in 2017, the PBC was tasked with the secretariat of China's newly established Financial Stability and Development Committee chaired by Vice Premier Liu He. In 2020, the PBC initiated supervision of significant financial holding companies.

The PBC underwent through another major restructuring in 2023, with the abolition of the nine regional branches established in 1998, which had already seen their authority watered down by a change in 2004 that had returned authority to the PBC's branches at the provincial level and further changes in 2018. Additionally, the PBC's county-level branches were absorbed by city-level branches. The new branches were inaugurated on August 18, 2023. The oversight over financial holding companies and financial consumer protection was also transferred from the PBC to the newly established National Financial Regulatory Administration (NFRA). Around 1,600 county-level branches of the PBC are planned to be absorbed to the NFRA; the PBC had 1,761 such branches at the end of 2021.

Management
The PBC is a cabinet-level executive department of the State Council. The top management of the PBC are composed of the governor and a certain number of deputy governors. The governor is nominated by the premier of the State Council, who is then approved by the National People's Congress or its Standing Committee and appointed by the president.The deputy governors of the PBC are appointed to or removed from office by the premier.

The PBC adopts the governor responsibility system under which the governor supervises the overall work of the PBC while the deputy governors provide assistance to the governor to fulfill his or her responsibility. The current governor is Pan Gongsheng. Deputy governors of the management team include: Zhu Hexin, Zhang Qingsong, Xuan Changneng, Lu Lei, and Tao Ling.

The PBC does not have central bank independence and is politically required to implement the policies of the Chinese Communist Party (CCP). It operates under the direction of the CCP's Central Financial Commission. The CCP committee secretary of the PBC is the most powerful position in the bank and can hold more sway than the governor. The current CCP committee secretary is Pan Gongsheng.

Structure

The PBC has branches in each 31 provincial-level administrative divisions in China, branches in five cities (Shenzhen, Dalian, Ningbo, Qingdao, and Xiamen), and 317 branches in prefecture-level divisions. It has 6 overseas representative offices (PBC Representative Office for America, PBC Representative Office (London) for Europe, PBC Tokyo Representative Office, PBC Frankfurt Representative Office, PBC Representative Office for Africa, Liaison Office of the PBC in the Caribbean Development Bank).

The PBC Monetary Policy Committee is an advisory body chaired by the PBC governor. It typically includes the directors and deputy directors of other financial agencies, as well as a few influential academic economists.

Departments
, the PBC consisted of functional departments (bureaus) as below:

 * General Administration Department (General Office of the CCP PBC Committee)
 * Legal Affairs Department
 * Monetary Policy Department
 * Macroprudential Policy Bureau
 * Financial Market Department
 * Financial Stability Bureau
 * Statistics and Analysis Department
 * Accounting and Treasury Department
 * Payment System Department
 * Technology Department
 * Currency, Gold and Silver Bureau
 * State Treasury Bureau
 * International Department
 * Internal Auditing Department
 * Human Resources Department (Organization Division of the CCP PBC Committee)
 * Research Bureau
 * Credit Information System Bureau
 * Anti-Money Laundering Bureau (Security Bureau)
 * Financial Consumer Protection Bureau
 * Education Department of the CCP PBC Committee
 * CCP Committee of the PBC Head Office (Office of Inspections)
 * Retired Staff Management Bureau
 * Office of Senior Advisors
 * Staff Union Committee
 * Youth League

The following enterprises and institutions were directly under the PBC as of 2012:

 * China Anti-Money Laundering Monitoring and Analysis Center
 * PBC Graduate School
 * China Financial Publishing House
 * Financial News
 * China National Clearing Center
 * China Banknote Printing and Minting Corporation
 * China Gold Coin Incorporation
 * China Financial Computerization Corporation
 * China Foreign Exchange Trade System

The PBC is active in promoting financial inclusion policy and a member of the Alliance for Financial Inclusion.

Head office
The head office building of the PBC, on West Chang'an Avenue, was constructed in 1987–1990 on a design by a team of architects led by Zhou Ru. While its materials are modern, its shape refers to two traditional Chinese motifs, namely yuanbao ingots and "wealth vases" (Jùbǎopén) from Chinese folklore.

title: People's Bank of China


text:
Rules of chess

The rules of chess (also known as the laws of chess) govern the play of the game of chess. Chess is a two-player abstract strategy board game. Each player controls sixteen pieces of six types on a chessboard. Each type of piece moves in a distinct way. The object of the game is to checkmate the opponent's king; checkmate occurs when a king is threatened with capture and has no escape. A game can end in various ways besides checkmate: a player can resign, and there are several ways a game can end in a draw.

While the exact origins of chess are unclear, modern rules first took form during the Middle Ages. The rules continued to be slightly modified until the early 19th century, when they reached essentially their current form. The rules also varied somewhat from region to region. Today, the standard rules are set by FIDE (Fédération Internationale des Échecs), the international governing body for chess. Slight modifications are made by some national organizations for their own purposes. There are variations of the rules for fast chess, correspondence chess, online chess, and Chess960.

Besides the basic moves of the pieces, rules also govern the equipment used, time control, conduct and ethics of players, accommodations for physically challenged players, and recording of moves using chess notation. Procedures for resolving irregularities that can occur during a game are provided as well.

Initial setup
Chess is played on a chessboard, a square board divided into a grid of 64 squares (eight-by-eight) of alternating color (similar to the board used in draughts). Regardless of the actual colors of the board, the lighter-colored squares are called "light" or "white", and the darker-colored squares are called "dark" or "black". Sixteen "white" and sixteen "black" pieces are placed on the board at the beginning of the game. The board is placed so that a white square is in each player's near-right corner. Horizontal rows are called ', and vertical columns are called '.

Each player controls sixteen pieces:

At the beginning of the game, the pieces are arranged as shown in the diagram: for each side one king, one queen, two rooks, two bishops, two knights, and eight pawns. The pieces are placed, one per square, as follows: Popular mnemonics used to remember the setup are "queen on her own color" and "white on right". The latter refers to setting up the board so that the square closest to each player's right is white.
 * Rooks are placed on the outside corners, right and left edge.
 * Knights are placed immediately inside of the rooks.
 * Bishops are placed immediately inside of the knights.
 * The queen is placed on the central square of the same color of that of the piece: white queen on the white square and black queen on the black square.
 * The king takes the vacant spot next to the queen.
 * Pawns are placed one square in front of all of the other pieces.

Gameplay
The player controlling the white pieces is named "White"; the player controlling the black pieces is named "Black". White moves first, then players alternate moves. Making a move is required; it is not legal to skip a move, even when having to move is detrimental. Play continues until a king is checkmated, a player resigns, or a draw is declared, as explained below. In addition, if the game is being played under a time control, a player who exceeds the time limit loses the game unless they cannot be checkmated.

The official chess rules do not include a procedure for determining who plays White. Instead, this decision is left open to tournament-specific rules (e.g. a Swiss system tournament or round-robin tournament) or, in the case of casual play, mutual agreement, in which case some kind of random choice such as flipping a coin can be employed. A common method is for one player to conceal a pawn of each color in either hand; the other player chooses a hand to open and receives the color of the piece that is revealed.

Basic moves
Each type of chess piece has its own method of movement. A piece moves to a vacant square except when an opponent's piece.

Except for any move of the knight and castling, pieces cannot jump over other pieces. A piece is captured (or taken) when an attacking enemy piece replaces it on its square. The captured piece is thereby permanently removed from the game. The king can be put in check but cannot be captured (see below).
 * The king moves exactly one square horizontally, vertically, or diagonally. A special move with the king known as castling is allowed only once per player, per game (see below).
 * A rook moves any number of vacant squares horizontally or vertically. It also is moved when castling.
 * A bishop moves any number of vacant squares diagonally. (Thus a bishop can move to only light or dark squares, not both.)
 * The queen moves any number of vacant squares horizontally, vertically, or diagonally.
 * A knight moves to one of the nearest squares not on the same, , or . (This can be thought of as moving two squares horizontally then one square vertically, or moving one square horizontally then two squares vertically—i.e. in an "L" pattern.) The knight is not blocked by other pieces; it jumps to the new location.
 * Pawns have the most complex rules of movement:
 * A pawn moves straight forward one square, if that square is vacant. If it has not yet moved, a pawn also has the option of moving squares straight forward, provided both squares are vacant. Pawns cannot move backwards.
 * A pawn, unlike other pieces, captures differently from how it moves. A pawn can capture an enemy piece on either of the two squares diagonally in front of the pawn. It cannot move to those squares when vacant except when capturing en passant.
 * The pawn is also involved in the two special moves en passant and promotion.

Castling
Castling consists of moving the king two squares towards a rook, then placing the rook on the other side of the king, adjacent to it. Castling is only permissible if all of the following conditions hold:
 * The king and rook involved in castling must not have previously moved;
 * There must be no pieces between the king and the rook;
 * The king may not currently be under attack, nor may the king pass through or end up in a square that is under attack by an enemy piece (though the rook is permitted to be under attack and to pass over an attacked square);
 * The castling must be or  as shown in the diagram.

An unmoved king and an unmoved rook of the same color on the same rank are said to have castling rights.

En passant
When a pawn advances two squares on its initial move and ends the turn adjacent to an enemy pawn on the same, it may be captured en passant by the enemy pawn as if it had moved only one square. This capture is legal only on the move immediately following the pawn's advance. The diagrams demonstrate an instance of this: if the white pawn moves from a2 to a4, the black pawn on b4 can capture it en passant, moving from b4 to a3, and the white pawn on a4 is removed from the board.

Promotion
If a player advances a pawn to its eighth rank, the pawn is then promoted (converted) to a queen, rook, bishop, or knight of the same color at the choice of the player (a queen is usually chosen). The choice is not limited to previously pieces. Hence it is theoretically possible for a player to have up to nine queens or up to ten rooks, bishops, or knights if all of the player's pawns are promoted.

Check
A king is in check when it is under attack by at least one enemy piece. A piece unable to move because it would place its own king in check (it is pinned against its own king) may still deliver check to the opposing player.

It is illegal to make a move that places or leaves one's king in check. The possible ways to get out of check are:
 * the king to a square where it is not in check.
 * the checking piece.
 * a piece between the king and the opponent's threatening piece ( the check).

In informal games, it is customary to announce "check" when making a move that puts the opponent's king in check. In formal competitions, however, check is rarely announced.

Checkmate
If a player's king is placed in check and there is no legal move that player can make to escape check, then the king is said to be checkmated, the game ends, and that player loses. Unlike the other pieces, the king is never captured.

The diagram shows an example checkmate position. The white king is threatened by the black queen; the empty square to which the king could move is also threatened; and the king cannot capture the queen, because it would then be in check by the rook.

Resigning
Either player may resign at any time, conceding the game to the opponent. To indicate resignation, the player may say "I resign". Tipping over the king also indicates resignation, but it should be distinguished from accidentally knocking the king over. Stopping both clocks is not an indication of resigning, since clocks can be stopped to call the arbiter. An offer of a handshake is sometimes used, but it could be mistaken for a draw offer.

Under FIDE Laws, a resignation by one player results in a draw if their opponent has no way to checkmate them via any series of legal moves, or a loss by that player otherwise.

Draws
The game ends in a draw if any of these conditions occur:
 * The player to move is not in check and has no legal move. This situation is called a stalemate. An example of such a position is shown in the adjacent diagram.
 * The game reaches a dead position.
 * Both players agree to a draw after one of the players makes such an offer.

In addition, in the FIDE rules, if a player has run out of time (see below), or has resigned, but the position is such that there is no way for the opponent to give checkmate by any series of legal moves, the game is a draw.

FIDE's competitive rules of play allow a player to claim a draw in either of two situations: These rules help prevent games from being extended indefinitely in tournaments.
 * Fifty moves have been made by each player without a capture or promotion of a pawn (this is the fifty-move rule);
 * The same position has appeared three times (or has appeared twice and the player claiming the draw can force the third appearance); this is the threefold repetition rule.

There is no longer a rule specifically defining perpetual check as a draw. In such a situation, either the threefold repetition rule or the fifty-move rule will eventually come into effect. More often, the players will simply agree to a draw.

Dead position
A dead position is defined as a position where neither player can checkmate their opponent's king by any sequence of legal moves. According to the rules of chess the game is immediately terminated the moment a dead position appears on the board.

Some basic endings are always dead positions; for example:
 * king against king;
 * king against king and bishop;
 * king against king and knight.

Blocked positions can arise in which progress is impossible for either side, such as the diagrammed position; these too are dead positions.

USCF rules, for games played under a time control that does not include delay or increment, allow draw claims for "insufficient losing chances". For example, if each player has only a king and a knight, checkmate is only achievable with the co-operation of both players, even if it is not a dead position.

Touch-move rule
The touch-move rule is a fundamental principle in chess, ensuring that players commit to moves deliberated mentally, without physically experimenting on the board. According to this rule, a player who touches a piece with the intention of moving it must then move it if legally possible. This rule also applies to capturing: a player who touches an opponent's piece must capture it if a legal capture is available. Special considerations apply for castling and pawn promotion, reflecting their unique nature in the game.

A player who touches a piece to adjust its physical position within a square must first alert the opponent by saying J'adoube or "I adjust". Once the game has started, only the player with the move may touch the pieces on the board.

Competitive rules of play
The following rules are applicable to games in organized tournaments and matches, sanctioned by FIDE. They mention timing (chess clocks), arbiters (or, in USCF play, directors), keeping score, and adjournment. The FIDE Laws of Chess define the rules for standard chess, rapid chess, blitz chess, and guidelines for Chess960. For standard chess, the players must record the moves, which is optional in rapid chess and blitz Chess. Some rules are specifically adapted for blind and visually impaired players.

These rules are used for (OTB) games. The rules for correspondence chess are defined by the ICCF. Rules for computer chess and for online chess played on a computer device are published by other organizers and governing bodies.

Moving the pieces
Although the touch-move rule is generally observed even in non-organized, non-sanctioned play, the interpretation of that rule to special situations such as capturing, castling, and promotion is not obvious; thus it is elaborated further in FIDE rules.

The movement of pieces is to be done with one hand. Once the hand is taken off a piece after moving it, the move cannot be retracted unless the. As for the touch-move rule, an arbiter who observes a violation of this rule must intervene immediately.

When castling, a player should first move the king with one hand and then move the rook with the same hand. In the case of a promotion, if a player releases the pawn on the eighth rank, the player must promote the pawn. After the pawn has moved, the player may touch any piece not on the board and the promotion is not finalized until the new piece is released on the promotion square. Although it is a common practice in informal play, under FIDE rules an upturned rook may not be used to represent a promoted queen; such a move would be treated as a legal rook promotion. If the correct piece is not immediately available, the player may stop the clocks and call the arbiter.

Timing
Tournament games are played under time constraints, called time controls, using a chess clock. Each player is timed separately and must make moves within the time control or forfeit the game. There are different types of time controls applied. For standard chess, different periods can be defined with different fixed times (e.g. first 40 moves in 100 minutes, next 20 moves in 50 minutes, remaining moves in 15 minutes). For rapid and blitz chess, only one period can be defined where all moves must be performed. Additionally, an increment or delay per move may be defined.
 * When a player runs out of time, this event is called . A flag-fall has no consequences unless stated as observed by the arbiter, in which case the arbiter must intervene, or claimed by a player.
 * When no flag-fall is stated, and one of the following events occur, the result of the game still holds. It is of no relevance if the player runs out of time afterwards, or has already run out of time, but this was not stated:
 * If a player delivers a checkmate, the game is over and that player wins.
 * If a move results in a stalemate, dead position, fivefold repetition or the seventy-five-move rule applies, the game is over and the game is drawn.
 * If a player correctly claims flag-fall, that player wins. But if the claiming player is out of time, or could not still theoretically checkmate the opponent, the game is a draw.

The United States Chess Federation (USCF) rule is different. USCF Rule 14E defines "insufficient material to win on time", that is lone king, king plus knight, king plus bishop, and king plus two knights opposed by no pawns, and there is no forced win in the final position. Hence to win on time with this material, the USCF rule requires that a win can be forced from that position, while the FIDE rule merely requires a win to be possible. (See Monika Soćko rules appeal in 2008 and Women's World Chess Championship 2008 for a famous instance of this rule.)

With mechanical clocks only, flag-fall for both players can occur. With digital clocks, the clock indicates which flag fell first, and this information is valid.

In the last period of a standard chess game or rapid games, if played without increment, a special set of rules applies regarding the clock, referenced as "Quickplay Finishes". These rules allow a player with under two minutes time to request an increment introduced, or request a draw based on claiming no progress or no effort, to be ruled by the arbiter. These rules have been relevant when playing with mechanical clocks, which do not allow setting an increment and are today with digital clocks of second importance only, as playing with increment is recommended.

Recording moves

Each square of the chessboard is identified with a unique pair of a letter and a number. The vertical are labeled  through, from White's left (i.e. the queenside) to White's right. Similarly, the horizontal are numbered from  to, starting from the one nearest White's side of the board. Each square of the board, then, is uniquely identified by its file letter and rank number. The white king, for example, starts the game on square e1. The black knight on b8 can move to a6 or c6.

In formal competition, each player is obliged to record each move as it is played in algebraic chess notation in order to settle disputes about illegal positions, overstepping time control, and making claims of draws by the fifty-move rule or repetition of position. Moves recorded in any other systems of notation cannot be used in evidence in such a dispute. Other chess notation systems include ICCF numeric notation for international correspondence chess and descriptive chess notation, formerly standard in English speaking countries. The current rule is that a move must be made on the board before it is written on paper or recorded with an electronic device.

Both players should indicate offers of a draw by writing "=" at that move on their score sheets. Notations about the time on the clocks can be made. A player with less than five minutes left to complete all the remaining moves is not required to record the moves (unless a delay of at least thirty seconds per move is being used). The score sheet must be made available to the at all times. A player may respond to an opponent's move before writing it down.

Adjournment

Formerly common, adjournments are no longer standard practice in chess competition.

When an adjournment is made, the player whose move it is writes their next move on their scoresheet but does not make the move on the chessboard. This is referred to as a. Both opponents' scoresheets are then placed in the sealed-move envelope and the envelope is sealed. The names of the players, the colors, the position, the time on the clocks and other game data are recorded on the envelope; the envelope may also be signed by both players. The arbiter then keeps possession of the envelope until it is time to restart the game, at which time the arbiter opens the envelope, makes the sealed move on the board, and starts the opponent's clock.

Illegal move
An illegal move is a move not made according to a piece's possible defined movements or made according to its possible movements but such that its own king is left or placed in check. Furthermore, pressing the clock without making a move or making a move with two hands is considered and penalized as an illegal move.

A player who makes an must retract that move and make a legal move. That move must be made with the same piece if possible, because the touch-move rule applies. If the illegal move was an attempt to castle, the touch-move rule applies to the king but not to the rook. If the mistake is noticed, the game should be restarted from the position in which the error occurred. The arbiter should adjust the time on the clock according to the best evidence. Some regional organizations have different rules.

A player may correct an illegal move if the player has not pressed the clock. In standard chess, if a move is found during the game, the position immediately before the irregularity is reinstated. In the most used form of rapid chess and blitz chess if the move is found before the opponent moves, the position immediately before the irregularity is also reinstated.

According to the FIDE Laws of Chess, the first stated completed illegal move results in a time penalty. The time penalty consists of giving the opponent two minutes extra time in standard chess, or one minute extra time in rapid or blitz. The second stated completed illegal move by the same player results in the loss of the game, unless the position is such that it is impossible for the opponent to win by any series of legal moves (e.g. if the opponent has a bare king) in which case the game is drawn. A move is completed when it has been made and the player has pressed the clock.

Under USCF rules, if a player completes an illegal move in blitz chess, the player's opponent may claim a win before making a move (if the opponent has enough material to win). One way to claim this win is to take a King left in check by the opponent. Once the illegal move has been answered, the move stands.

Incorrect setup
For standard chess and the most used form of rapid and blitz chess there are the following rules. If it is discovered during the game that the starting position was incorrect, the game is restarted. If it is discovered during the game that the board is oriented incorrectly, the game is continued with the pieces transferred to a correctly oriented board. If the game starts with colors reversed, the game is restarted if less than 10 moves have been made by both players, otherwise the game is continued. If the clock setting is found to be incorrect during the game, it is corrected according to best judgement. Some regional organizations have different rules.

Piece displacement
If a player knocks over pieces, it is the same player's responsibility to restore them to their correct positions, on that player's time. If it is discovered that an illegal move has been made, or that pieces have been displaced, the game is restored to the position before the irregularity. If that position cannot be determined, the game is restored to the last known correct position.

Illegal position
An illegal position is a position which cannot be reached by any series of legal moves.

Conduct
Players may not use any notes, outside sources of information (including computers), or advice from other people. Analysis on another board is not permitted. Scoresheets are to record objective facts about the game only, such as time on the clock or draw offers. Players may not leave the competition area without permission of the arbiter.

High standards of etiquette and ethics are expected. Players should shake hands before and after the game. Generally a player should not speak during the game, except to offer a draw, resign, or to call attention to an irregularity. An announcement of "check" is commonly made in informal games but is not recommended in officially sanctioned games. A player may not distract or annoy another player by any means, including repeatedly offering a draw.

Due to increasing concerns about the use of chess engines and outside communication, mobile phone usage is banned. The first forfeit by a high-profile player, for phone ringing during play, occurred in 2003. In 2014 FIDE extended this to ban all mobile phones from the playing area during chess competitions, under penalty of forfeiture of the game or even expulsion from the tournament. The rules allow for less rigid enforcement in minor events.

Equipment
Pieces of the Staunton chess set design are the standard and are usually made of wood or plastic. They are often black and white; other colors may be used (like a dark wood or even red for the dark pieces) but they would still be called the "white" and "black" pieces (see White and Black in chess). The height of the king should be about 95 mm, within 10 percent. The diameter of the king should be 40 to 50% of its height. The size of the other pieces should be in proportion to the king. The pieces should be well balanced.

The size of the squares of the chessboard should be approximately 1.25 to 1.3 times the diameter of the base of the king, or 50 to 65 mm. Squares of approximately 57 mm ($3 3/8$ inches) normally are well-suited for pieces with the kings in the preferred size range; four pawns should fit on a square. Squares may be the natural color of the wood, or other combinations of dark and light colors.

In games subject to time control, a chess clock is used, consisting of two adjacent clocks and buttons to stop one clock while starting the other, such that the two component clocks never run simultaneously. The clock can be analog or digital though a digital clock is preferred under both USCF and FIDE rulesets. This is because most tournaments now include either an increment (extra time being added prior or after the move) or delay (a countdown to when a clock starts again) to their time controls. Before the start of the game, in FIDE competitions the arbiter decides where the chess clock is placed; in USCF competitions the director may decide, or the director may leave it to the players, in which case the player with the black pieces will decide.

History
The rules of chess have evolved much over the centuries from the early chess-like games played in India in the 6th century. For much of that time the rules have varied from area to area. The modern rules first took form in southern Europe during the 13th century, giving more mobility to pieces that previously had more restricted movement (such as the queen and bishop). Such modified rules entered into an accepted form during the late 15th century or early 16th century. The basic moves of the king, rook, and knight are unchanged. A pawn originally did not have the option of moving two squares on its first move, and promoted only to a queen upon reaching the eighth rank. The queen was originally the fers or farzin, which could move one square diagonally in any direction. In European chess it became able to leap two squares diagonally, forwards, backwards, or to left or right on its first move; some areas also gave this right to a newly promoted pawn. In the Persian and Arabic game the bishop was a pīl (Persian) or fīl (Arabic) (meaning "elephant") which moved two squares diagonally with jump. In the Middle Ages the pawn could only be promoted to the equivalent of a queen (which at that time was a weak piece) if it reached its eighth rank. During the 12th century, the squares on the board sometimes alternated colors, and this became the standard in the 13th century; whence the word "chequered"/"checkered". Between 1200 and 1600 several laws emerged that drastically altered the game. Checkmate became a requirement to win; a player could not win by capturing all of the opponent's pieces. Stalemate was added, although the outcome has changed several times (see History of the stalemate rule). Pawns gained the option of moving two squares on their first move, and the en passant rule was a natural consequence of that new option. The king and rook acquired the right to castle (see for different versions of the rule).

Between 1475 and 1500, the queen and the bishop also acquired their current moves, which made them much stronger pieces. When all of these changes were accepted, the game was in essentially its modern form.

The rules for promotion have changed several times. As stated above, originally the pawn could only be promoted to the queen, which at that time was a weak piece. When the queen acquired its current move and became the most powerful piece, the pawn could then be promoted to a queen or a rook, bishop, or knight. In the 18th century rules allowed only the promotion to a piece already captured, e.g. the rules published in 1749 by François-André Danican Philidor. In the 19th century, this restriction was lifted, which allowed for a player to have more than one queen, e.g. the 1828 rules by Jacob Sarratt.

Two new rules concerning draws were introduced, each of which has changed through the years:
 * The threefold repetition rule was added, although at some times up to six repetitions have been required, and the exact conditions have been specified more clearly (see ).
 * The fifty-move rule was also added. At various times, the number of moves required was different, such as 24, 60, 70, or 75. For several years in the 20th century, the standard fifty moves was extended to one hundred moves for a few specific endgames (see Fifty-move rule's history).

Another group of new laws included (1) the touch-move rule and the accompanying "j'adoube/adjust" rule; (2) that White moves first (in 1889 ); (3) the orientation of the board; (4) the procedure if an illegal move was made; (5) the procedure if the king had been left in check for some moves; and (6) issues regarding the behavior of players and spectators. The Staunton chess set was introduced in 1849 and it became the standard style of pieces. The size of pieces and squares of the board was standardized.

Until the middle of the 19th century, chess games were played without any time limit. In an 1834 match between Alexander McDonnell and Louis-Charles Mahé de La Bourdonnais, McDonnell took an inordinate amount of time to move, sometimes up to 1½ hours. In 1836 Pierre Charles Fournier de Saint-Amant suggested a time limit, but no action was taken. At the 1851 London tournament, Staunton blamed his loss in his match against Elijah Williams on Williams' slow play; one game was adjourned for the day after only 29 moves. The next year a match between Daniel Harrwitz and Johann Löwenthal used a limit of 20 minutes per move. The first use of a modern-style time limit was in an 1861 match between Adolph Anderssen and Ignác Kolisch.

Codification
The first known publication of chess rules was in a book by Luis Ramírez de Lucena about 1497, shortly after the movement of the queen, bishop, and pawn were changed to their modern form. Ruy López de Segura gave rules of chess in his 1561 book Libro de la invencion liberal y arte del juego del axedrez. In the 16th and 17th centuries, there were local differences concerning rules such as castling, promotion, stalemate, and en passant. Some of these differences persisted until the 19th century; for example, differences in castling rules persisted in Italy until the late 19th century.

As chess clubs arose and tournaments became common, there was a need to formalize the rules. In 1749 Philidor (1726–1795) wrote a set of rules that were widely used, as well as rules by later writers such as the 1828 rules by Jacob Sarratt (1772–1819) and rules by George Walker (1803–1879). In the 19th century, many major clubs published their own rules, including The Hague in 1803, London in 1807, Paris in 1836, and St. Petersburg in 1854. In 1851 Howard Staunton (1810–1874) called for a "Constituent Assembly for Remodeling the Laws of Chess" and proposals by Tassilo von Heydebrand und der Lasa (1818–1889) were published in 1854. Staunton had published rules in Chess Player's Handbook in 1847, and his new proposals were published in 1860 in Chess Praxis; they were generally accepted in English-speaking countries. German-speaking countries usually used the writings of chess authority Johann Berger (1845–1933) or Handbuch des Schachspiels by Paul Rudolf von Bilguer (1815–1840), first published in 1843.

In 1924, Fédération Internationale des Échecs (FIDE) was formed and in 1928 it took up the task of standardizing the rules. At first FIDE tried to establish a universal set of rules, but translations to various languages differed slightly. Although FIDE rules were used for international competition under their control, some countries continued to use their own rules internally. In 1952, FIDE created the Permanent Commission for the Rules of Chess (also known as the Rules Commission) and published a new edition of the rules. The third official edition of the laws was published in 1966. The first three editions of the rules were published in French, with that as the official version. In 1974 FIDE published the English version of the rules (which was based on an authorized 1955 translation). With that edition, English became the official language of the rules. Another edition was published in 1979. Throughout this time, ambiguities in the laws were handled by frequent interpretations that the Rules Commission published as supplements and amendments. In 1982, the Rules Commission rewrote the laws to incorporate the interpretations and amendments. In 1984, FIDE abandoned the idea of a universal set of laws, although FIDE rules are the standard for high-level play. With the 1984 edition, FIDE implemented a four-year moratorium between changes to the rules. Other editions were issued in 1988 and 1992.

The rules of national FIDE affiliates (such as the United States Chess Federation, or USCF) are based on the FIDE rules, with slight variations. Some other differences are noted above. Kenneth Harkness published popular rulebooks in the United States starting in 1956, and the USCF continues to publish rulebooks for use in tournaments it sanctions.

In 2008, FIDE added the variant Chess960 to the appendix of the "Laws of Chess". Chess960 uses a random initial set-up of main pieces, with the conditions that the king is placed somewhere between the two rooks, and bishops on opposite-color squares. The castling rules are extended to cover all these positions.

In the 21st century, rules about such things as mobile phones and unauthorized use of chess engines were introduced.

Customizations in tournament play
Under FIDE's Laws of Chess, tournament organizers have the option to parameterize some rules to fit their events. This flexibility covers time controls for standard, rapid, and blitz chess, and setting the 'default time' - the period before a player forfeits for being late, which is zero unless otherwise specified. Additionally, measures can be introduced to discourage players from agreeing to short draws. One such case was the "no drawing or resigning during the first 30 moves" rule used at the 2009 London Chess Classic.

title: Rules of chess