text:
Talk:Dowism

For a March 2005 deletion debate over this page see Votes for deletion/Dowism

The article, it say:

 * The intentional misspelling is well represented in this verse from a Monty Python song

 * I like Chineese food
 * The waiters are never rude
 * Think of the many things they've done to impress
 * There's Maoism, Dowism, Eching and chess

Why is this last line not "Daoism, I-Ching and chess"? Is it in a lyrics book spelled like this? I can find one website which uses the spelling we have here, but that also misspells the name of the song as "I Like Chineese", (with two Es in the middle) which is definitely wrong (I just checked my album sleeve). There are many more websites with the "correct" spelling. I'll remove this reference unless somebody justifies it. Oh, and just to kick an article when it's down - isn't it "the waiters never are rude" rather than "are never"? :) --Camembert

And (there's more) I've just listened to the record, and it sounds like "Taoism" more than "Daoism" anyway. Sorry, but I'm removing it. --Camembert

title: Talk:Dowism


text:
Papias of Hierapolis

Papias (Παπίας) was a Greek Apostolic Father, Bishop of Hierapolis (modern Pamukkale, Turkey), and author who lived c. 60 – c. 130 AD He wrote the Exposition of the Sayings of the Lord (Λογίων Κυριακῶν Ἐξήγησις) in five books. This work, which is lost apart from brief excerpts in the works of Irenaeus of Lyons (c. 180) and Eusebius of Caesarea (c. 320), is an important early source on Christian oral tradition and especially on the origins of the canonical Gospels.

Life
Very little is known of Papias apart from what can be inferred from his own writings. He is described as "an ancient man who was a hearer of John and a companion of Polycarp" by Polycarp's disciple Irenaeus (c. 180).

Eusebius adds that Papias was Bishop of Hierapolis around the time of Ignatius of Antioch. In this office Papias was presumably succeeded by Abercius of Hierapolis.

The name Papias was very common in the region, suggesting that he was probably a native of the area.

Date
The work of Papias is dated by a few modern scholars to about 95–110. Later dates were once argued from two references that now appear to be mistaken. One dating Papias' death to around the death of Polycarp in 164 is actually a mistake for Papylas. Another unreliable source in which Papias is said to refer to the reign of Hadrian (117–138) seems to have resulted from confusion between Papias and Quadratus of Athens.

Eusebius refers to Papias only in his third book, and thus seems to date him before the opening of his fourth book in 109. Papias himself knows several New Testament books, whose dates are themselves controversial, and was informed by John the Evangelist, Aristion, the daughters of Philip and others who had themselves heard the Twelve Apostles. He is also called a companion of the long-lived Polycarp (69–155), Agapius of Hierapolis dates one of his histories to the 12th year of Trajan's rule (110 AD). For all these reasons, Papias is thought to have written around the turn of the 2nd century.

Fragments
Despite indications that the work of Papias was still extant in the late Middle Ages, the full text is now lost. Extracts, however, appear in a number of other writings, some of which cite a book number. MacDonald proposes the following tentative reconstruction of the five books, following a presumed Matthaean order.

• # Preface and John's Preaching

• # Preface

• # Gospel origins

• # Those called children (Book 1)

• # Jesus in Galilee

• # The sinful woman

• # Paradise and the Church

• # The deaths of James and John (Book 2)

• # Jesus in Jerusalem

• # The Millennium

• # The Passion

• # Agricultural bounty in the Kingdom (Book 4)

• # The death of Judas (Book 4)

• # The fall of the angels

• # After the Resurrection

• # Barsabbas drinking poison

• # The raising of Manaem's mother

Gospel origins

Papias provides the earliest extant account of who wrote the Gospels. Eusebius preserves two (possibly) verbatim excerpts from Papias on the origins of the Gospels, one concerning Mark and then another concerning Matthew.

On Mark, Papias cites John the Elder: "The Elder used to say: Mark, in his capacity as Peter’s interpreter, wrote down accurately as many things as he recalled from memory—though not in an ordered form—of the things either said or done by the Lord. For he neither heard the Lord nor accompanied him, but later, as I said, Peter, who used to give his teachings in the form of chreiai, but had no intention of providing an ordered arrangement of the logia of the Lord. Consequently Mark did nothing wrong when he wrote down some individual items just as he related them from memory. For he made it his one concern not to omit anything he had heard or to falsify anything."

The excerpt regarding Matthew says only: "Therefore Matthew put the logia in an ordered arrangement in the Hebrew language, but each person interpreted them as best he could."

How to interpret these quotations from Papias has long been a matter of controversy, as the original context for each is missing and the Greek is in several respects ambiguous and seems to employ technical rhetorical terminology. It has been questioned if Papias is even referring to the canonical Gospels bearing those names. However Eusebius, who had the complete text and context before him, understood Papias in these passages to be referring to the canonical Gospels.

The word logia (λόγια)—which also appears in the title of Papias' work—is itself problematic. In non-Christian contexts, the usual meaning was oracles, but since the 19th century it has been interpreted as sayings, which sparked numerous theories about a lost "Sayings Gospel", now called Q, resembling the Gospel of Thomas. But the parallelism implies a meaning of things said or done, which suits the canonical Gospels well.

The apparent claim that Matthew wrote in Hebrew—which in Greek could refer to either Hebrew or Aramaic—is echoed by many other ancient authorities. Modern scholars have proposed numerous explanations for this assertion, in light of the prevalent view that canonical Matthew was composed in Greek and not translated from Semitic. One theory is that Matthew himself produced firstly a Semitic work and secondly a recension of that work in Greek. Another is that others translated Matthew into Greek rather freely. Another is that Papias simply means "Ἑβραΐδι διαλέκτῳ" as a Hebrew style of Greek. Another is that Papias refers to a distinct work now lost, perhaps a sayings collection like Q or the so-called Gospel according to the Hebrews. Yet another is that Papias was simply mistaken.

As for Mark, the difficulty has been in understanding the relationship described between Mark and Peter—whether Peter recalled from memory or Mark recalled Peter's preaching, and whether Mark translated this preaching into Greek or Latin or merely expounded on it, and if the former, publicly or just when composing the Gospel; modern scholars have explored a range of possibilities. Eusebius, after quoting Papias, goes on to say that Papias also cited 1 Peter, where Peter speaks of "my son Mark", as corroboration. Within the 2nd century, this relation of Peter to Mark's Gospel is alluded to by Justin and expanded on by Clement of Alexandria.

We do not know what else Papias said about these or the other Gospels—he certainly treated John —but some see Papias as the likely unattributed source of at least two later accounts of the Gospel origins. Bauckham argues that the Muratorian Canon (c. 170) has drawn from Papias; the extant fragment, however, preserves only a few final words on Mark and then speaks about Luke and John. Hill argues that Eusebius' earlier account of the origins of the four Gospels is also drawn from Papias.

Eschatological
Eusebius concludes from the writings of Papias that he was a chiliast, understanding the Millennium as a literal period in which Christ will reign on Earth, and chastises Papias for his literal interpretation of figurative passages, writing that Papias "appears to have been of very limited understanding", and felt that his misunderstanding misled Irenaeus and others.

Irenaeus indeed quotes the fourth book of Papias for an otherwise-unknown saying of Jesus, recounted by John the Evangelist, which Eusebius doubtless has in mind:

"The Lord used to teach about those times and say: 'The days will come when vines will grow, each having ten thousand shoots, and on each shoot ten thousand branches, and on each branch ten thousand twigs, and on each twig ten thousand clusters, and in each cluster ten thousand grapes, and each grape when crushed will yield twenty-five measures of wine. And when one of the saints takes hold of a cluster, another cluster will cry out, 'I am better, take me, bless the Lord through me.' Similarly a grain of wheat will produce ten thousand heads, and every head will have ten thousand grains, and every grain ten pounds of fine flour, white and clean. And the other fruits, seeds, and grass will produce in similar proportions, and all the animals feeding on these fruits produced by the soil will in turn become peaceful and harmonious toward one another, and fully subject to humankind.… These things are believable to those who believe.' And when Judas the traitor did not believe and asked, 'How, then, will such growth be accomplished by the Lord?', the Lord said, 'Those who live until those times will see.'"

Parallels have often been noted between this account and Jewish texts of the period such as 2 Baruch.

On the other hand, Papias is elsewhere said to have understood mystically the Hexaemeron (six days of Creation) as referring to Christ and the Church.

Pericope Adulterae

Eusebius concludes his account of Papias by saying that he relates "another account about a woman who was accused of many sins before the Lord, which is found in the Gospel according to the Hebrews". Agapius of Hierapolis (10th century) offers a fuller summary of what Papias said here, calling the woman an adulteress. The parallel is clear to the famous Pericope Adulterae, a problematic passage absent or relocated in many ancient Gospel manuscripts. The parallel is not exact since, in the version know to Papias, the woman "was accused of many sins", unlike the account found in the Pericope Adulterae in which her accusers simply say that she was "caught in the act of adultery." The remarkable fact is that the story is known in some form to such an ancient witness as Papias.

What is less clear is to what extent Eusebius and Agapius are reporting the words of Papias versus the form of the pericope known to them from elsewhere. A wide range of versions have come down to us, in fact. Since the passage in John is virtually unknown to the Greek patristic tradition; Eusebius has cited the only parallel he recognized, from the now-lost Gospel according to the Hebrews, which may be the version quoted by Didymus the Blind.

The nearest agreement with "many sins" actually occurs in the Johannine text of Armenian codex Matenadaran 2374 (formerly Ečmiadzin 229); this codex is also remarkable for ascribing the longer ending of Mark to "Ariston the Elder", which is often seen as somehow connected with Papias.

Death of Judas
According to a scholium attributed to Apollinaris of Laodicea, Papias also related a tale on the grotesque fate of Judas Iscariot:

"Judas did not die by hanging but lived on, having been cut down before he choked to death. Indeed, the Acts of the Apostles makes this clear: 'Falling headlong he burst open in the middle and his intestines spilled out.' Papias, the disciple of John, recounts this more clearly in the fourth book of the Exposition of the Sayings of the Lord, as follows:

'Judas was a terrible, walking example of ungodliness in this world, his flesh so bloated that he was not able to pass through a place where a wagon passes easily, not even his bloated head by itself. For his eyelids, they say, were so swollen that he could not see the light at all, and his eyes could not be seen, even by a doctor using an optical instrument, so far had they sunk below the outer surface. His genitals appeared more loathsome and larger than anyone else's, and when he relieved himself there passed through it pus and worms from every part of his body, much to his shame. After much agony and punishment, they say, he finally died in his own place, and because of the stench the area is deserted and uninhabitable even now; in fact, to this day one cannot pass that place without holding one's nose, so great was the discharge from his body, and so far did it spread over the ground.'"

Death of John
Two late sources (Philip of Side and George Hamartolus) cite the second book of Papias as recording that John and his brother James were killed by the Jews. However, some modern scholars doubt the reliability of the two sources regarding Papias, while others argue that Papias did speak of John's martyrdom. According to the two sources, Papias presented this as fulfillment of the prophecy of Jesus on the martyrdom of these two brothers. This is consistent with a tradition attested in several ancient martyrologies.

Barsabbas
Papias relates, on the authority of the daughters of Philip, an event concerning Justus Barsabbas, who according to Acts was one of two candidates proposed to join the Twelve Apostles. The summary in Eusebius tells us that he "drank a deadly poison and suffered no harm," while Philip of Side recounts that he "drank snake venom in the name of Christ when put to the test by unbelievers and was protected from all harm." The account about Justus Barsabbas is followed by a one about the resurrection of the mother of a certain Manaem. This account may be connected to a verse from the longer ending of Mark: "They will pick up snakes in their hands, and if they drink any deadly thing, it will not hurt them."

Reliability
Eusebius had a "low esteem of Papias' intellect", but knew that Irenaeus believed Papias to be a reliable witness to original apostolic traditions.

We should be hesitant to take much from Eusebius' comment about Papias' intellect though. Eusebius’ use of sources suggests that he himself did not always exercise the soundest of critical judgement, and his negative assessment of Papias was in all likelihood dictated simply by a distrust of chiliasm.

Modern scholars have debated Papias' reliability. Much discussion of Papias's comments about the Gospel of Mark and Gospel of Matthew is concerned with either showing their reliability as evidence for the origins of these Gospels or with emphasizing their apologetic character in order to discredit their reliability. Yoon-Man Park cites a modern argument that Papias's tradition was formulated to vindicate the apostolicity of Mark's Gospel, but dismisses this as an unlikely apologetic route unless the Peter-Mark connection Papias described had already been accepted with general agreement by the early church. Maurice Casey argued that Papias was indeed reliable about a Hebrew collection of sayings by Matthew the Apostle, which he argues was independent of the Greek Gospel of Matthew, possibly written by another Matthew or Matthias in the early church.

Others argue Papias faithfully recorded what was related to him, but misunderstood the subjects of narrations he was unfamiliar with.

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

title: Papias of Hierapolis


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Morley Callaghan

Edward Morley Callaghan  (February 22, 1903 – August 25, 1990) was a Canadian novelist, short story writer, playwright, and TV and radio personality.

Biography
Of Canadian/English-immigrant parentage, Callaghan was born and raised in Toronto, Ontario. In his youth, he played baseball for Canadian Sports Hall of Fame coach, Bob Abate, and pitched for Abate's Arlington baseball team. He was educated at Withrow PS, Riverdale Collegiate Institute, the University of Toronto and Osgoode Hall Law School. He articled and was called to the Bar, but did not practice law. During the 1920s he worked at the Toronto Star where he became friends with a fellow reporter Ernest Hemingway, formerly of The Kansas City Star. Callaghan began writing stories that were well received and soon were recognized as one of the best short story writers of the day. In 1929 he spent some months in Paris, where he was part of the great gathering of writers in Montparnasse that included Ernest Hemingway, Ezra Pound, Gertrude Stein, F. Scott Fitzgerald, and James Joyce.

Callaghan's novels and short stories are marked by undertones of Roman Catholicism, often focusing on individuals whose essential characteristic is a strong but often weakened sense of self. His first novel was Strange Fugitive (1928); several short stories, novellas, and novels followed. Callaghan published little between 1937 and 1950 - an artistically dry period. However, during these years, many non-fiction articles were written in various periodicals such as New World (Toronto), and National Home Monthly. Luke Baldwin's Vow, a slim novel about a boy and his dog, was originally published in a 1947 edition of Saturday Evening Post and soon became a juvenile classic read in school rooms around the world. The Loved and the Lost (1951) won the Governor General's Award. Callaghan's later works include, among others, The Many Colored Coat (1960), A Passion in Rome (1961), A Fine and Private Place (1975), A Time for Judas (1983), Our Lady of the Snows (1985). His last novel was A Wild Old Man Down the Road (1988). Publications of short stories have appeared in The Lost and Found Stories of Morley Callaghan (1985) and in The New Yorker Stories (2001). The four-volume The Complete Stories (2003) collects for the first time 90 of his stories.

Callaghan was also a contributor to The New Yorker, Harper's Bazaar, Maclean's, Esquire, Cosmopolitan, Saturday Evening Post, Yale Review, New World, Performing Arts in Canada, and Twentieth Century Literature.

Callaghan married Loretto Dee, with whom he had two sons: Michael (born November 1931) and Barry (born 1937), a poet and author in his own right. Barry Callaghan's memoir Barrelhouse Kings (1998), examines his career and that of his father. After outliving most of his contemporaries, Callaghan died after a brief illness in Toronto at the age of 87. He was interred in Mount Hope Catholic Cemetery in Ontario.

Recognition
Callaghan was awarded the Royal Society of Canada's Lorne Pierce Medal in 1960. In 1982 he was made a Companion of the Order of Canada.

Morley Callaghan is the subject of a CBC Television Life and Times episode, and the CBC mini-series, Hemingway Vs. Callaghan, which first aired in March 2003.

From 1951 until he died in 1990, the author had lived in the Rosedale, Toronto area, at 20 Dale Avenue. A historic plaque at the nearby Glen Road footbridge summarizes Callaghan's noteworthy writing career and the most significant of his literary contemporaries, including Ernest Hemingway and F Scott Fitzgerald.

Commemorative postage stamp
On September 8, 2003, to commemorate the 50th anniversary of the National Library of Canada, Canada Post released a special commemorative series, "The Writers of Canada", with a design by Katalina Kovats, featuring two English-Canadian and two French-Canadian stamps. Three million stamps were issued. Callaghan was chosen for one of the English-Canadian stamps.

Novels

 * Strange Fugitive - 1928
 * It's Never Over - 1930
 * A Broken Journey - 1932
 * Such Is My Beloved - 1934
 * They Shall Inherit the Earth - 1935
 * More Joy in Heaven - 1937
 * The Loved and the Lost - 1951
 * The Many Colored Coat - 1960 (reissued as The Man with the Coat, 1988)
 * A Passion in Rome - 1961
 * A Fine and Private Place - 1975
 * A Time for Judas - 1983
 * Our Lady of the Snows - 1985 (based on his novella The Enchanted Pimp)
 * A Wild Old Man on the Road - 1988

Novellas

 * No Man's Meat - 1931
 * Luke Baldwin's Vow - 1948 (reissued as The Vow, 2006)
 * The Varsity Story - 1948
 * An Autumn Penitent - 1973 (and In His Own Country)
 * Close to the Sun Again - 1977
 * No Man's Meat and The Enchanted Pimp - 1978

Short fiction

 * A Native Argosy - 1929
 * Now That April's Here and Other Stories - 1936
 * Morley Callaghan's Stories - 1959
 * Stories - 1967
 * The Lost and Found Stories of Morley Callaghan - 1985
 * The Morley Callaghan Reader - 1997
 * The New Yorker Stories - 2001
 * The Complete Stories (four volumes) - 2003
 * Ancient Lineage and Other Stories - 2012
 * The Snob
 * The Sentimentalists

Non-fiction

 * That Summer in Paris: Memories of Tangled Friendships with Hemingway, Fitzgerald and Some Others - 1963
 * Winter - 1974

Plays

 * Turn Again Home (based on the novel They Shall Inherit the Earth, produced in New York City in 1940, and produced under the title Going Home in Toronto in 1950)
 * Just Ask George (produced in Toronto, 1940)
 * To Tell the Truth (produced in Toronto, 1949)
 * Season of the Witch - 1976

Film adaptations

 * Now That April's Here (1958)
 * The Cap (1984)

Books

 * Boire, Gary A., Morley Callaghan and His Works - 1990
 * Boire, Gary A., Morley Callaghan: Literary Anarchist - 1994
 * Cameron, Donald, Conversations with Canadian Novelists, Part Two - 1973
 * Contemporary Literary Criticism, Volume 3 - 1975
 * Contemporary Literary Criticism, Volume 14 - 1980
 * Contemporary Literary Criticism, Volume 41 - 1987
 * Contemporary Literary Criticism, Volume 65 - 1991
 * Dictionary of Literary Biography, Volume 68: Canadian Writers, 1920–1959, First Series - 1988
 * Morley, Patricia, Morley Callaghan - 1978
 * Orange, John, Orpheus in Winter: Morley Callaghan's The Loved and the Lost - 1993
 * Sutherland, Fraser, The Style of Innocence - 1972
 * Wilson, Edmund, O Canada - 1965
 * Woodcock, George, Moral Predicament: Morley Callaghan's More Joy in Heaven - 1993

Periodicals

 * Books in Canada, April, 1986, pp. 32–33.
 * Canadian Forum, March, 1960; February, 1968.
 * Canadian Literature, summer, 1964
 * Canadian Literature, winter, 1984, pp. 66–69.
 * Canadian Literature, autumn, 1990, pp. 148–49.
 * Dalhousie Review, autumn, 1959.
 * Essays on Canadian Writing, winter, 1984–85, pp. 309– 15
 * Essays on Canadian Writing, summer, 1990, pp. 16–20.
 * Form and Century, April, 1934.
 * New Republic, February 9, 1963.
 * New Yorker, November 26, 1960.
 * Queen's Quarterly, autumn, 1957
 * Queen's Quarterly, autumn, 1989, pp. 717–19.
 * Saturday Night, October, 1983, pp. 73–74.
 * Tamarack Review, winter, 1962.
 * American Spectator, February, 1991.

title: Morley Callaghan


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User:Robharper

I'm a computer tinkerer, polyobsessive, and occasional Wikipedian. Not much to say, really.

title: User:Robharper


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User talk:Robharper

Hello there Robharper, welcome to the 'pedia! I hope you like the place and decide to stay. If you ever need editing help visit How does one edit a page and experiment at Sandbox. If you need pointers on how we title pages visit Naming conventions or how to format them visit our manual of style. If you have any other questions about the project then check out Help or add a question to the Village pump. Cheers! --maveric149

title: User talk:Robharper


text:
Pulmonary alveolus

A pulmonary alveolus (: alveoli, from Latin alveolus, "little cavity"), also known as an air sac or air space, is one of millions of hollow, distensible cup-shaped cavities in the lungs where pulmonary gas exchange takes place. Oxygen is exchanged for carbon dioxide at the blood–air barrier between the alveolar air and the pulmonary capillary. Alveoli make up the functional tissue of the mammalian lungs known as the lung parenchyma, which takes up 90 percent of the total lung volume.

Alveoli are first located in the respiratory bronchioles that mark the beginning of the respiratory zone. They are located sparsely in these bronchioles, line the walls of the alveolar ducts, and are more numerous in the blind-ended alveolar sacs. The acini are the basic units of respiration, with gas exchange taking place in all the alveoli present. The alveolar membrane is the gas exchange surface, surrounded by a network of capillaries. Oxygen is diffused across the membrane into the capillaries and carbon dioxide is released from the capillaries into the alveoli to be breathed out.

Alveoli are particular to mammalian lungs. Different structures are involved in gas exchange in other vertebrates.

Structure
The alveoli are first located in the respiratory bronchioles as scattered outpockets, extending from their lumens. The respiratory bronchioles run for considerable lengths and become increasingly alveolated with side branches of alveolar ducts that become deeply lined with alveoli. The ducts number between two and eleven from each bronchiole. Each duct opens into five or six alveolar sacs into which clusters of alveoli open.

Each terminal respiratory unit is called an acinus and consists of the respiratory bronchioles, alveolar ducts, alveolar sacs, and alveoli. New alveoli continue to form until the age of eight years.

A typical pair of human lungs contains about 480 million alveoli, providing a total surface area for gas exchange of between 70 and 80 square metres. Each alveolus is wrapped in a fine mesh of capillaries covering about 70% of its area. The diameter of an alveolus is between 200 and 500 μm.

Microanatomy
An alveolus consists of an epithelial layer of simple squamous epithelium (very thin, flattened cells), and an extracellular matrix surrounded by capillaries. The epithelial lining is part of the alveolar membrane, also known as the respiratory membrane, that allows the exchange of gases. The membrane has several layers – a layer of alveolar lining fluid that contains surfactant, the epithelial layer and its basement membrane; a thin interstitial space between the epithelial lining and the capillary membrane; a capillary basement membrane that often fuses with the alveolar basement membrane, and the capillary endothelial membrane. The whole membrane however is only between 0.2 μm at its thinnest part and 0.6 μm at its thickest.

In the alveolar walls there are interconnecting air passages between the alveoli known as the pores of Kohn. The alveolar septum that separates the alveoli in the alveolar sac contains some collagen fibers and elastic fibers. The septa also house the enmeshed capillary network that surrounds each alveolus. The elastic fibres allow the alveoli to stretch when they fill with air during inhalation. They then spring back during exhalation in order to expel the carbon dioxide-rich air.

There are three major types of alveolar cell. Two types are pneumocytes or pneumonocytes known as type I and type II cells found in the alveolar wall, and a large phagocytic cell known as an alveolar macrophage that moves about in the lumens of the alveoli, and in the connective tissue between them. Type I cells, also called type I pneumocytes, or type I alveolar cells, are squamous, thin and flat and form the structure of the alveoli. Type II cells, also called type II pneumocytes or type II alveolar cells, release pulmonary surfactant to lower surface tension, and can also differentiate to replace damaged type I cells.

Development
Development of the earliest structures that will contain alveoli begins on day 22 and is divided into five stages: embryonic, pseudoglandular, canalicular, saccular, and alveolar stage. The alveolar stage begins approximately 36 weeks into development. Immature alveoli appear as bulges from the sacculi which invade the primary septa. As the sacculi develop, the protrusions in the primary septa become larger; new septations are longer and thinner and are known as secondary septa. Secondary septa are responsible for the final division of the sacculi into alveoli. Majority of alveolar division occurs within the first 6 months but continue to develop until 3 years of age. To create a thinner diffusion barrier, the double-layer capillary network fuse into one network, each one closely associated with two alveoli as they develop.

In the first three years of life, the enlargement of lungs is a consequence of the increasing number of alveoli; after this point, both the number and size of alveoli increases until the development of lungs finishes at approximately 8 years of age.

Type I cells
Type I cells are the larger of the two cell types; they are thin, flat epithelial lining cells (membranous pneumocytes), that form the structure of the alveoli. They are squamous (giving more surface area to each cell) and have long cytoplasmic extensions that cover more than 95% of the alveolar surface.

Type I cells are involved in the process of gas exchange between the alveoli and blood. These cells are extremely thin – sometimes only 25 nm – the electron microscope was needed to prove that all alveoli are lined with epithelium. This thin lining enables a fast diffusion of gas exchange between the air in the alveoli and the blood in the surrounding capillaries.

The nucleus of a type I cell occupies a large area of free cytoplasm and its organelles are clustered around it reducing the thickness of the cell. This also keeps the thickness of the blood-air barrier reduced to a minimum.

The cytoplasm in the thin portion contains pinocytotic vesicles which may play a role in the removal of small particulate contaminants from the outer surface. In addition to desmosomes, all type I alveolar cells have occluding junctions that prevent the leakage of tissue fluid into the alveolar air space.

The relatively low solubility (and hence rate of diffusion) of oxygen necessitates the large internal surface area (about 80 square m [96 square yards]) and very thin walls of the alveoli. Weaving between the capillaries and helping to support them is an extracellular matrix, a meshlike fabric of elastic and collagenous fibres. The collagen fibres, being more rigid, give the wall firmness, while the elastic fibres permit expansion and contraction of the walls during breathing.

Type I pneumocytes are unable to replicate and are susceptible to toxic insults. In the event of damage, type II cells can proliferate and differentiate into type I cells to compensate.

Type II cells
Type II cells are cuboidal and much smaller than type I cells. They are the most numerous cells in the alveoli, yet do not cover as much surface area as the squamous type I cells. Type II cells (granulous pneumocytes) in the alveolar wall contain secretory organelles known as lamellar bodies or lamellar granules, that fuse with the cell membranes and secrete pulmonary surfactant. This surfactant is a film of fatty substances, a group of phospholipids that reduce alveolar surface tension. The phospholipids are stored in the lamellar bodies. Without this coating, the alveoli would collapse. The surfactant is continuously released by exocytosis. Reinflation of the alveoli following exhalation is made easier by the surfactant, which reduces surface tension in the thin fluid lining of the alveoli. The fluid coating is produced by the body in order to facilitate the transfer of gases between blood and alveolar air, and the type II cells are typically found at the blood–air barrier.

Type II cells start to develop at about 26 weeks of gestation, secreting small amounts of surfactant. However, adequate amounts of surfactant are not secreted until about 35 weeks of gestation – this is the main reason for increased rates of infant respiratory distress syndrome, which drastically reduces at ages above 35 weeks gestation.

Type II cells are also capable of cellular division, giving rise to more type I and II alveolar cells when the lung tissue is damaged.

MUC1, a human gene associated with type II pneumocytes, has been identified as a marker in lung cancer.

The importance of the type 2 lung alveolar cells in the development of severe respiratory symptoms of COVID-19 and potential mechanisms on how these cells are protected by the SSRIs fluvoxamine and fluoxetine was summarized in a review in April 2022.

Alveolar macrophages
The alveolar macrophages reside on the internal luminal surfaces of the alveoli, the alveolar ducts, and the bronchioles. They are mobile scavengers that serve to engulf foreign particles in the lungs, such as dust, bacteria, carbon particles, and blood cells from injuries. They are also called pulmonary macrophages, and dust cells.

Surfactant
Insufficient surfactant in the alveoli is one of the causes that can contribute to atelectasis (collapse of part or all of the lung). Without pulmonary surfactant, atelectasis is a certainty. The severe condition of acute respiratory distress syndrome (ARDS) is caused by a deficiency or dysfunction of surfactant. Insufficient surfactant in the lungs of preterm infants causes infant respiratory distress syndrome (IRDS). The lecithin–sphingomyelin ratio is a measure of fetal amniotic fluid to indicate lung maturity or immaturity. A low ratio indicates a risk factor for IRDS. Lecithin and sphingomyelin are two of the glycolipids of pulmonary surfactant.

Impaired surfactant regulation can cause an accumulation of surfactant proteins to build up in the alveoli in a condition called pulmonary alveolar proteinosis. This results in impaired gas exchange.

Inflammation
Pneumonia is an inflammatory condition of the lung tissue, which can be caused by both viruses and bacteria. Cytokines and fluids are released into the alveolar cavity, interstitium, or both, in response to infection, causing the effective surface area of gas exchange to be reduced. In severe cases where cellular respiration cannot be maintained, supplemental oxygen may be required.
 * Diffuse alveolar damage can be a cause of acute respiratory distress syndrome(ARDS) a severe inflammatory disease of the lung.
 * In asthma, the bronchioles become narrowed, causing the amount of air flow into the lung tissue to be greatly reduced. It can be triggered by irritants in the air, photochemical smog for example, as well as substances to which a person is allergic.
 * Chronic bronchitis occurs when an abundance of mucus is produced by the lungs. The production of mucus occurs naturally when the lung tissue is exposed to irritants. In chronic bronchitis, the air passages into the alveoli, the respiratory bronchioles, become clogged with mucus. This causes increased coughing in order to remove the mucus, and is often a result of extended periods of exposure to cigarette smoke.
 * Hypersensitivity pneumonitis

Structural

Almost any type of lung tumor or lung cancer can compress the alveoli and reduce gas exchange capacity. In some cases the tumor will fill the alveoli.
 * Cavitary pneumonia is a process in which the alveoli are destroyed and produce a cavity. As the alveoli are destroyed, the surface area for gas exchange to occur becomes reduced. Further changes in blood flow can lead to decline in lung function.
 * Emphysema is another disease of the lungs, whereby the elastin in the walls of the alveoli is broken down by an imbalance between the production of neutrophil elastase (elevated by cigarette smoke) and alpha-1 antitrypsin (the activity varies due to genetics or reaction of a critical methionine residue with toxins including cigarette smoke). The resulting loss of elasticity in the lungs leads to prolonged times for exhalation, which occurs through passive recoil of the expanded lung. This leads to a smaller volume of gas exchanged per breath.
 * Pulmonary alveolar microlithiasis is a rare lung disorder of small stone formation in the alveoli.

Fluid
A pulmonary contusion is a bruise of the lung tissue caused by trauma. Damaged capillaries from a contusion can cause blood and other fluids to accumulate in the tissue of the lung, impairing gas exchange.

Pulmonary edema is the buildup of fluid in the parenchyma and alveoli. An edema is usually caused by left ventricular heart failure, or by damage to the lung or its vasculature.

Coronavirus
Because of the high expression of angiotensin-converting enzyme 2 (ACE2) in type II alveolar cells, the lungs are susceptible to infections by some coronaviruses including the viruses that cause severe acute respiratory syndrome (SARS) and coronavirus disease 2019 (COVID-19).

title: Pulmonary alveolus


text:
Rules of Go

The rules of Go have seen some variation over time and from place to place. This article discusses those sets of rules broadly similar to the ones currently in use in East Asia. Even among these, there is a degree of variation.

Notably, Chinese and Japanese rules differ in a number of aspects. The most significant of these are the scoring method, together with attendant differences in the manner of ending the game.

While differences between sets of rules may have moderate strategic consequences on occasion, they do not change the character of the game. The different sets of rules usually lead to the same game result, so long as the players make minor adjustments near the end of the game. Differences in the rules are said to cause problems in perhaps one in every 10,000 games in competition.

This article first presents a simple set of rules which are, except for wording, identical to those usually referred to as the Tromp–Taylor Rules, themselves close in most essential respects to the Chinese rules. These rules are then discussed at length, in a way that does not assume prior knowledge of Go on the part of the reader. The discussion is for the most part applicable to all sets of rules, with exceptions noted. Later sections of the article address major areas of variation in the rules of go, and individual sets of rules.

Basic rules
A set of rules suitable for beginners is presented here. The rules are studied more fully in below.

Two statements of the same basic rules, differing only in wording, are given here. The first is a concise one due to James Davies. The second is a formulation of the basic rules used for expository purposes in this article.

Except for terminology, the basic rules are identical to the Logical Rules first proposed in their current form in September 1996 by John Tromp and Bill Taylor. They are also quite close to the Simplified Ing Rules of the European Go Federation, the only exception being the method of ending the game.

Concise statement
These rules appear in "The Rules and Elements of Go" by James Davies. They assume familiarity with the equipment used to play go, for which one may refer to below.

Notes: The words move and territory are used differently here than elsewhere in this article; play and area, respectively, are used instead. A clarification to rule 5 is added in parentheses.
 * 1) The board is empty at the onset of the game (unless players agree to place a handicap).
 * 2) Black makes the first move, after which White and Black alternate.
 * 3) A move consists of placing one stone of one's own color on an empty intersection on the board.
 * 4) A player may pass their turn at any time.
 * 5) A stone or solidly connected group of stones of one color is captured and removed from the board when all the intersections directly adjacent to it are occupied by the enemy. (Capture of the enemy takes precedence over self-capture.)
 * 6) No stone may be played so as to recreate a former board position.
 * 7) Two consecutive passes end the game.
 * 8) A player's area consists of all the points the player has either occupied or surrounded.
 * 9) The player with more area wins.

These rules rely on common sense to make notions such as "connected group" and "surround" precise. What is here called a "solidly connected group of stones" is also called a chain.

Reference statement
The basic rules are formulated here in a more detailed way to ease their presentation in below. (Each rule and definition links to a detailed explanation in that section.)

An optional rule prohibiting suicide is included as Rule 7A.

Players and equipment

 * Rule 1. Players: Go is a game between two players, called Black and White.
 * Rule 2. Board: Go is played on a plain grid of 19 horizontal and 19 vertical lines, called a board.
 * Definition.("Intersection", "Adjacent") A point on the board where a horizontal line meets a vertical line is called an intersection. Two intersections are said to be adjacent if they are connected by a horizontal or vertical line with no other intersections between them.
 * Rule 3. Stones: Go is played with playing tokens known as stones. Each player has at their disposal an adequate supply (usually 180) of stones of the same color.

Positions

 * Rule 4. Positions: At any time in the game, each intersection on the board is in one and only one of the following three states: 1) empty; 2) occupied by a black stone; or 3) occupied by a white stone. A position consists of an indication of the state of each intersection.
 * Definition. ("Connected") Two placed stones of the same color (or two empty intersections) are said to be connected if it is possible to draw a path from one intersection to the other by passing through adjacent intersections of the same state (empty, occupied by white, or occupied by black).
 * Definition. ("Liberty") In a given position, a liberty of a stone is an empty intersection adjacent to that stone or adjacent to a stone which is connected to that stone.

Play

 * Rule 5. Initial position: At the beginning of the game, the board is empty.
 * Rule 6. Turns: Black moves first. The players alternate thereafter.
 * Rule 7. Moving: When it is their turn, a player may either pass (by announcing "pass" and performing no action) or play. A play consists of the following steps (performed in the prescribed order):
 * Step 1. (Playing a stone) Placing a stone of their color on an empty intersection (chosen subject to Rule 8 and, if it is in effect, to Optional Rule 7A). It can never be moved to another intersection after being played.
 * Step 2. (Capture) Removing from the board any stones of their opponent's color that have no liberties.
 * Step 3. (Self-capture) Removing from the board any stones of their own color that have no liberties.
 * Optional Rule 7A. Prohibition of suicide: A play is illegal if one or more stones of that player's color would be removed in Step 3 of that play.
 * Rule 8. Prohibition of repetition: A play is illegal if it would have the effect (after all steps of the play have been completed) of creating a position that has occurred previously in the game.

End

 * Rule 9. End: The game ends when both players have passed consecutively. The final position is the position on the board at the time the players pass consecutively.
 * Definition. ("Territory") In the final position, an empty intersection is said to belong to a player's territory if all stones adjacent to it or to an empty intersection connected to it are of that player's color.
 * Definition. ("Area") In the final position, an intersection is said to belong to a player's area if either: 1) it belongs to that player's territory; or 2) it is occupied by a stone of that player's color.
 * Definition. ("Score") A player's score is the number of intersections in their area in the final position.
 * Rule 10. Winner: If one player has a higher score than the other, then that player wins. Otherwise, the game is a draw.

Comparative features of the basic rules
The essential features of these basic rules relative to other rulesets are summarized here. Each of the differences is discussed in greater detail in a later section of the article.

What variation exists among rulesets concerns primarily Rules 7A, 8, 9 and 10.

 * The basic rules use area scoring, as in China and Taiwan, and as in the official rules of many Western countries. The main alternative is territory scoring. Though territory scoring is the system used in Japan and Korea, and is customarily used in the West, it is not possible to use territory scoring unless Rule 9 is replaced by a much more complex end-of-game rule. The goal of these basic rules is to present a simple system first. See below.
 * The basic rules require the players to "play the game out" entirely. Virtually all rulesets used in practice provide some mechanism that allows players to begin scoring the game before the final position (the one used to score the game) has been reached. In some cases, this is merely a convenience intended to save time. In others, it may be an essential feature of the game. In any case, explaining these rules might obscure the nature of the game somewhat for a person unfamiliar with it. See below.
 * The basic rules allow suicide (or self-capture). This is unusual outside of Taiwan and New Zealand. Inclusion of Optional Rule 7A is in line with practice elsewhere. See below.
 * The basic rules apply the rule of positional superko. This, or a similar rule, is common in official Western rulesets, but not in East Asia. See below.
 * The basic rules do not contain any special exceptions for territory in a seki. This agrees with most practice outside Japan and Korea. See below.
 * The basic rules do not have a komi. This is now unusual in even-strength games, but was common practice until the mid-twentieth century. A komi is a number of points, usually five to eight, awarded to White in compensation for moving second. See below.
 * The basic rules make no provision for the use of handicap stones. See below.
 * The basic rules do not specify a counting system. A counting system is a conventional method for calculating the difference in score between the players (hence determining the winner). It may incorporate various devices, such as filling in one's territory after the game, or shifting stones on the board into patterns, which allow quicker calculation of the difference in scores.

Explanation of the basic rules
The object of the game of go is, in rough terms, to control more territory at the end of the game than one's opponent does.

Players
'''Rule 1. Go is a game between two players, called Black and White.'''

The choice of black or white is traditionally done by chance between players of even strength. The method of selection is called nigiri. One player (A) takes a handful of white stones; the other player (B) then places either one or two black stones on the board, indicating "even" or "odd". Player A counts the number stones in their hand to determine whether there is an odd or even number. If the number of stones matches the other player's selection of "even" or "odd", Player B will play the black stones; if not, they will take the white stones.

When players are of different strengths, the weaker player takes black. Black may also pre-place several handicap stones before play begins, to compensate for the difference in strength—see below.

Board
'''Rule 2. Go is played on a plane grid of 19 horizontal and 19 vertical lines, called a board.'''

'Definition: A point on the board where a horizontal line meets a vertical line is called an intersection''. Two intersections are said to be adjacent if they are distinct and connected by a horizontal or vertical line with no other intersections between them.'''

The condition that the intersections be "distinct" is included to ensure that an intersection is not considered to be adjacent to itself.

Intersections are also called points.

There are 361 points on a regular 19 × 19 board.

For simplicity, the rules will be illustrated mostly using 5 × 5 boards.

Each of the following diagrams shows two points on a 5 × 5 board:

In the first two diagrams, the points are adjacent; in the third and fourth, they are not.

Though 19 × 19 boards are standard, go can be played on another size board. Particularly common sizes for quick games are 9 × 9 and 13 × 13. (See also "Board size" below.)

Beginners might prefer to play on a 9 × 9 board to start. The nature of the game remains similar enough to make this worthwhile, yet the games are shorter. For beginners, playing longer games is less important than playing a greater number of games.

Stones
'''Rule 3. Go is played with playing tokens known as stones. Each player has at their disposal an adequate supply of stones of their color.'''

Traditionally, Black is given 181 stones, and White, 180, to start the game. This is almost always sufficient, but if it turns out to be insufficient, extra stones will be used.

Positions
'''Rule 4. At any time in the game, each intersection on the board is in one and only one of the following three states: 1) empty; 2) occupied by a black stone; or 3) occupied by a white stone. A position consists of an indication of the state of each intersection.'''

Specifying a position involves only the current state of the board. It requires no indication of whose turn it is, nor any information relating to previous moves or states of the board. This definition of "position" is used in Rule 8 ("positional superko").

The diagram shows a possible position:

Naturally, two stones are said to be adjacent if they occupy adjacent intersections. Similarly, a stone and an intersection are adjacent if the stone occupies an intersection adjacent to that intersection.

Connected stones and points
'''Definition. Two placed stones of the same color (or two empty intersections) are said to be connected if it is possible to draw a path from one to the other by passing only through adjacent intersections of the same state (empty, occupied by white, or occupied by black).'''

The concept of connected stones is used to describe (via the concept of liberties, defined below) the conditions in which stones are captured by a move. The concept of connected empty points is used only at the end of the game, to define a player's score.

In the following position, the stones 1 and 7 are connected by the sequence of black stones 1, 2, ..., 7, in which each stone (other than 1) is adjacent to the stone before it. The empty points a and k are connected by the sequence of empty points a, b, ..., k, in which each point (other than a) is adjacent to the one before it. In fact, it is easy to see in this position that all the black stones are connected to each other and that all the empty points are connected to each other.

The following position can be used as an example for when stones and empty points are connected.

In the diagram, stones and empty points are marked with the same number or letter, respectively, whenever they are connected to each other.

A chain is a set of one or more stones (necessarily of the same color) that are all connected to each other and that are not connected to any other stones. Although it is not necessary to define the word chain in order to state the rules, the concept is important for an understanding of the game.

For example, Black and White each have four chains in the diagram above. Black has one three-stone chain, one two-stone chain, and two one-stone chains. White has one four-stone chain and three one-stone chains.

It follows from the definitions that any stone on the board belongs to exactly one chain. Furthermore, saying that two distinct stones of the same color are connected is the same as saying that they belong to the same chain.

Liberties
In a given position, a liberty of a stone is an empty intersection adjacent to that stone or adjacent to a stone which is connected to that stone.

For example:

In the above position, the points a, b, c, d, e, are the liberties of the black stone at 1.
 * a is a liberty of Black 1 because it is adjacent to Black 1 itself.
 * b is a liberty of Black 1 because it is adjacent to Black 2, which is connected to Black 1. Alternatively, b is adjacent to Black 3.
 * c is a liberty of Black 1 because it is adjacent to Black 3, which is connected to Black 1.
 * d is a liberty of Black 1 because it is adjacent to Black 4, which is connected to Black 1.
 * e is a liberty of Black 1 because it is adjacent to Black 5, which is connected to Black 1. Alternatively, e is adjacent to Black 4.

The results are the same when determining the liberties of Black 2, or of any other stone belonging to the black chain.

In this position:
 * The black stones marked 1 have the liberties c, d and h.
 * The black stones marked 2 have the liberties d, e, f, g and h.
 * The black stone marked 3 has the liberties g and h.
 * The white stones marked 4 have the liberties a, b and c.
 * The white stone marked 5 has the single liberty c.
 * The white stone marked 6 has the liberties d and h.
 * The white stone marked 7 has the liberties e and f.

Since the liberties of any two stones belonging to the same chain are identical, they are often called the liberties of that chain. For example, in the first diagram, the points a, b, c, d and e are the liberties of the lone black chain. In the second diagram, the liberties of the black chain in the lower right are c, d and h.

Initial position
'''Rule 5. At the beginning of the game, the board is empty.'''

Alternation of turns
'''Rule 6. Black moves first. The players alternate thereafter.'''

What players may do when they move is the object of Rules 7 and 8.

Moving
'''Rule 7. On their turn, a player may either pass (by announcing "pass" and performing no action) or play. A play consists of the following steps (performed in the prescribed order):'''
 * Step 1. Placing a stone of their color on an empty intersection (chosen subject to Rule 8 and, if it is in effect, to Optional Rule 7A).
 * Step 2. Removing from the board any stones of their opponent's color that have no liberties.
 * Step 3. Removing from the board any stones of their own color that have no liberties.

A move is defined as a play or a pass. Thus, on each turn a player moves once.

A player may pass on any move. Usually, passing is beneficial only at the end of the game, when all territory has been claimed and further moves would be useless, or even harmful to a player's position.

The following three sections discuss the successive steps of a play in greater detail, bearing in mind that, in view of Steps 2 and 3, all stones remaining on the board after any move must have at least one liberty.

Placing a stone on the board
'''Step 1 of a play. The player places a stone of their color on an empty intersection (chosen subject to Rule 8 and, if it is in effect, to Optional Rule 7A).'''

As indicated by the reference to Rules 8 and 7A (respectively the superko rule and prohibition of suicide, to be discussed later), there are some restrictions on the choice of point at which to play.

The following diagrams show a possible sequence of moves at the beginning of the game:

The following diagrams show how Black might play later in the same game:

Numbers are often used, as here, to indicate new moves in printed diagrams.

Once a stone has been played, it remains on the board in the same location, until the end of the game or until it is captured (removed from the board as part of Step 2 or Step 3 of a play).

Capture
'''Step 2 of a play. (After playing their stone) a player removes from the board any stones of their opponent's color that have no liberties.'''

The stones removed from the board are said to have been captured by the player moving.

The diagrams below show the capture of a white stone by Black. To begin with, the white stone has a single liberty at a. By playing a stone at a, Black removes the last remaining liberty of the white stone. It is subsequently removed from the board.

At the edge of the board and especially in the corners, stones have fewer liberties to start with and are more easily captured.

Next, White captures a chain of four black stones by playing at a.

Black captures the white chain by playing at a. The black stone is not captured, because the white stones are removed first, providing it with two liberties.

Black captures the marked white chain at the edge of the board by playing at a. Then White captures the black stone in the corner by playing at b.

Here, White captures the three marked black chains by playing at a.

Self-capture
'''Step 3 of a play. (After playing their stone and capturing any opposing stones) a player removes from the board any stones of their own color that have no liberties.'''

'Optional Rule 7A. A play is illegal if one or more stones would be removed in Step 3 of that play.'

The removal of one or more stones in Step 3 is called self-capture, or suicide. Most rulesets give effect to Optional Rule 7A, which prohibits it. This means that, in those rulesets, any play which under the basic rules would require a self-capture to be performed is illegal. For further information, see below.

First an example which, it is emphasized, does not involve self-capture. When Black plays at a, the capture of the marked white stones results in the black chain at the bottom right acquiring liberties. This move is legal (with the same result) whatever the rules.

The previous example shows that it is important that Step 2 of a play (capture) precedes Step 3 (self-capture). If the order were reversed, then self-capture would occur here.

It is not difficult to convince oneself that if a play results in the capture of opposing stones, self-capture does not occur.

Now some examples of plays in which self-capture occurs. These moves would be illegal under the optional rule prohibiting suicide.

In this example, if Black plays at a, then the stone played by them is removed immediately. This move has the same effect on the position as a pass, though it would not allow White to end the game by passing next (Rule 9). The move is in any event illegal by Rule 8. (This is the positional superko rule. This move might be legal under other versions of the superko rule. See below.)

In the next example, Black plays at a, resulting in the self-capture of the marked black stones.

Ko and Superko
'''Rule 8. A play is illegal if it would have the effect (after all steps of the play have been completed) of creating a position that has occurred previously in the game.'''

Though a pass is a kind of "move", it is not a "play". Therefore, Rule 8 never bars a player from passing. One consequence of Rule 8 is the so-called ko rule:

'''Consequence (ko rule). One may not play in such a way as to recreate the board position following one's previous move.'''

Whereas Rule 8 prohibits repetition of any previous position, the ko rule prohibits only immediate repetition.

The word ko, pronounced with a long "o", is taken from Japanese (劫, ; usually written with katakana: コウ) and can mean both "threat" and "aeon" (from the Buddhist kalpa).

Rule 8 is known as the positional superko rule. The word "positional" is used to distinguish it from slightly different superko rules that are sometimes used. While the ko rule is observed in all forms of go, not all rulesets have a superko rule. The practical effects of the ko rule and the superko rule are similar; situations governed by the superko rule but not by the ko rule arise relatively infrequently. For further information, see below. The superko rule is designed to ensure the game eventually comes to an end, by preventing indefinite repetition of the same positions. While its purpose is similar to that of the threefold repetition rule of Western chess, it differs from it significantly in nature; the superko rule bans moves that would cause repetition, whereas Western chess allows such moves as one method of forcing a draw. It is more similar to the prohibition of moves which would repeat the position in Chinese Chess (Xiangqi). The ko rule has important strategic consequences in go.

Some examples follow in which Rule 8 applies. These examples cover only the most important case, namely the ko rule.

The first diagram shows the board immediately after White has played at 1, and it is Black's turn. Black captures the marked white stone by playing at a. If White responds by capturing at b with 3, the board position is identical to that immediately following White 1. White 3 is therefore prohibited by the ko rule.

Another example of ko follows. Here, Black 3 is illegal by the ko rule.

As noted in the section "Self-capture", Rule 8 prohibits the suicide of a single stone. This is something of a triviality since such a move would not be strategically useful. Taking it for granted that no suicide of a single stone has occurred, the ko rule can be engaged in only one situation:

Restatement of the ko rule: One may not capture just one stone if that stone was played on the previous move and that move also captured just one stone.

Furthermore, this can occur only when one plays in the location at which one's stone was captured in the previous move. The two points where consecutive captures might occur, but for the ko rule, are said to be in ko. For example, in the first two diagrams above, the points a and b are in ko.

The next two examples involve capture and immediate recapture, but the ko rule is not engaged, because either the first or second capture takes more than one stone.

In the first diagram below, White must prevent Black from playing at a, and does this with 1 in the second diagram. Black can capture the three stones in White 1's group by playing at b. Black does this with Black 2 in the third diagram. White may recapture Black 2 by playing at a again, because the resulting position, shown in the fourth diagram, has not occurred previously. It differs from the position after White 1 by the absence of the two marked white stones.

In the first diagram below, it is White's turn. White must prevent Black from connecting the marked stones to the others by playing at a. The second diagram shows White's move. White is threatening to capture the marked black stones by playing at b. In the third diagram, Black plays at b to prevent this, capturing White 1. However, by playing at a again, White can capture Black 2's group. This is not barred by the ko rule because the resulting position, shown in the fourth diagram, differs from the one after White 1 by the absence of the marked black stones. This kind of capture is called a snapback.

Ko threats
The next example is typical of real games. It shows how the ko rule can sometimes be circumvented by first playing elsewhere on the board.

The first diagram below shows the position after Black 1. White can capture the marked black stone by playing at a. The second diagram shows the resulting position. Black cannot immediately recapture at b because of the ko rule. So Black instead plays 3 in the third diagram. For reasons that will become clear, Black 3 is called a "ko threat".

At this point, White could choose to connect at b, as shown in the first diagram below. However, this would be strategically unsound, because Black 5 would guarantee that Black could eventually capture the white group altogether, no matter how White played.

Instead, White responds correctly to Black 3 with 4 in the first diagram below. Now, contrary to the situation after White 2, Black can legally play at b, because the resulting position, shown in the second diagram, has not occurred previously. It differs from the position after Black 1 because of the presence of Black 3 and White 4 on the board. Now White is prohibited from recapturing at a by the ko rule. White has no moves elsewhere on the board requiring an immediate reply from Black (ko threats), so White plays the less urgent move 6, capturing the black stone at 3, which could not have evaded capture even if White had waited. In the next diagram, Black connects at a before White has a chance to recapture. Both players pass and the game ends in this position.

End
'''Rule 9. The game ends when both players have passed consecutively. The final position (the position later used to score the game) is the position on the board at the time the players pass consecutively.'''

Since the position on the board at the time of the first two consecutive passes is the one used to score the game, Rule 9 can be said to require the players to "play the game out".

Under Rule 9, players must for example capture enemy stones even when it may be obvious to both players that they cannot evade capture. Otherwise the stones are not considered to have been captured. Because Rule 9 differs significantly from the various systems for ending the game used in practice, a word must be said about them.

These systems, which are discussed more fully in below, generally allow the game to end as soon as it is clear to the players which stones would remain on the board if the game continued. The precise means of achieving this varies widely by ruleset, and in some cases has strategic implications. These systems often use passing in a way that is incompatible with Rule 9. For players, knowing the conventions surrounding the manner of ending the game in a particular ruleset can therefore have practical importance.

Under Chinese rules, and more generally under any using the area scoring system, a player who played the game out as if Rule 9 were in effect would not be committing any strategic errors by doing so. They would, however, likely be viewed as unsportsmanlike for prolonging the game unnecessarily. On the other hand, under a territory scoring system like that of the Japanese rules, playing the game out in this way would in most cases be a strategic mistake.

Territory
'''Definition. In the final position, an empty intersection is said to belong to a player's territory if all stones adjacent to it or to an empty intersection connected to it are of that player's color.'''

Note: Unless the entire board is empty, the second condition – that there be at least one stone of the kind required – is always satisfied and can be ignored.

A point can never belong to both players' territories.

On the other hand, it may well happen that an empty intersection belongs to neither player's territory. In that case the point is said to be neutral territory. There are rarely any more than a handful of neutral points at the end of a game; in the majority of cases, there are none at all.

Japanese and Korean rules count some points as neutral where the basic rules, like Chinese rules, would not. For more on this, see.

In order to understand the definition of territory, it is instructive to apply it first to a position of a kind that might arise before the end of a game.

The point a is adjacent to a black stone. Therefore, a does not belong to White's territory. However, a is connected to b (by the path shown in the diagram, among others), which is adjacent to a white stone. Therefore, a does not belong to Black's territory either. In conclusion, a is neutral territory.

The point c is connected to d, which is adjacent to a white stone. But c is also connected to e, which is adjacent to a black stone. Therefore, c is neutral territory.

Similarly, the points f and g are neutral territory.

On the other hand, h is adjacent only to black stones and is not connected to any other points. Therefore, h is black territory. For the same reason, i and j are black territory, and k is white territory.

It is because there is so much territory left to be claimed that skilled players would not end the game in the previous position. The game might continue with White playing 1 in the next diagram. If the game ended in this new position, the marked intersections would become White's territory, since they would no longer be connected to an empty intersection adjacent to a black stone.

The game might end with the moves shown below. In the final position, the points marked a are black territory and the points marked b are white territory. The point marked c is the only neutral territory left.

In Japanese and Korean rules, the point in the lower right corner and the point marked a on the right side of the board would fall under the seki exception, in which they would be considered neutral territory. (See below.)

Area
'''Definition. In the final position, an intersection is said to belong to a player's area if either: 1) it belongs to that player's territory; or 2) it is occupied by a stone of that player's color.'''

Consider once again the final position shown in the last diagram of the section "Territory". The following diagram illustrates the area of each player in that position. Points in a player's area are occupied by a stone of the corresponding color. The lone neutral point does not belong to either player's area.

Score
'''Definition. A player's score is the number of intersections in their area in the final position.'''

For example, if a game ended as in the last diagram in the section "Territory", the score would be: Black 44, White 36. The players' scores add to 80. The difference between this and the 81 intersections on a 9 × 9 board is accounted for by the one point of neutral territory. The scoring system described here is known as area scoring, and is the one used in the Chinese rules. Different scoring systems exist. These determine the same winner in most instances. See the Scoring systems section below.

Winner
'''Rule 10. If one player has a higher score than the other, then that player wins. Otherwise, the game is drawn.'''

In the previous example, Black wins by eight points.

Margin of victory does not matter; winning by one point is as good as winning by 100 points.

Scoring systems
The most prominent difference between rulesets is the scoring method. There are two main scoring systems: territory scoring (the Japanese method) and area scoring (the Chinese method). A third system (stone scoring) is rarely used today but was used in the past and has historical and theoretical interest.

Care should be taken to distinguish between scoring systems and counting methods. Only two scoring systems are in wide use, but there are two ways of counting using "area" scoring.

Territory scoring
In territory scoring (including Japanese and Korean rules) a player's score is determined by the number of empty locations that player has surrounded minus the number of stones their opponent has captured.

Furthermore, Japanese and Korean rules have special provisions in cases of seki, though this is not a necessary part of a territory scoring system. (See "Seki" below.)

Typically, counting is done by having each player place the prisoners they have taken into the opponent's territory and rearranging the remaining territory into easy-to-count shapes.

Territory scoring was how very old Chinese Go games were scored; Chinese style gradually switched to area scoring during the Yuan dynasty and Ming dynasty of the 13th–16th centuries.

Area scoring
In area scoring (including Chinese rules), a player's score is determined by the number of stones that player has on the board plus the empty area surrounded by that player's stones.

There are several common ways in which to count the score (all these ways will always result in the same winner):

 * The oldest counting method is as follows: At the end of the game, all white stones are removed from the board, and the players use black stones to fill the entirety of the black territory. Score is determined by counting the black stones. Since the board contains 361 intersections, black must have 181 or more stones to win. This method is still widely used in Mainland China.
 * Around 1975, Taiwanese player and industrialist Ing Chang-ki invented a method of counting now known as Ing counting. Each player begins the game with exactly 180 stones (Ing also invented special stone containers that count each player's stones). At the end, all stones are placed on the board. One vacant intersection will remain, appearing in the winner's area; the number of stones of one color in the other color's area will indicate the margin of victory.

Stone scoring
In stone scoring, a player's score is the number of stones that player has on the board. Play typically continues until both players have nearly filled their territories, leaving only the two eyes necessary to prevent capture. It seems to have arisen during the Ming Dynasty of China, but eventually its popularity faded.

Attempts at reconciling the scoring systems
If the game ends with both players having played the same number of times, then the score will be identical in territory and area scoring. AGA rules call for a player to give the opponent a stone when passing, and for White to play last (passing a third time if necessary). This "passing stone" does not affect the player's final area, but as it is treated like a prisoner in the territory scoring system, the result using a territory system is consequently the same as it would be using an area scoring system.

The results for stone and area scoring are identical if both sides have the same number of groups. Otherwise the results will differ by two points for each extra group. Some older rules used area scoring with a "group tax" of two points per group; this will give results identical to those with stone scoring.

Counting phase
Customarily, when players agree that there are no useful moves left (most often by passing in succession), they attempt to agree which groups are alive and which are dead. If disagreement arises, then under Chinese rules the players simply play on.

However, under Japanese rules, the game is already considered to have ended. The players attempt to ascertain which groups of stones would remain if both players played perfectly from that point on. (These groups are said to be alive.) In addition, this play is done under rules in which kos are treated differently from ordinary play. If the players reach an incorrect conclusion, then they both lose.

Unlike most other rulesets, the Japanese rules contain lengthy definitions of when groups are considered alive and when they are dead. In fact, these definitions do not cover every situation that may arise. Some difficult cases not entirely determined by the rules and existing precedent must be adjudicated by a go tribunal.

The need for the Japanese rules to address the definition of life and death follows from the fact that in the Japanese rules, scores are calculated by territory rather than by area. The rules cannot simply require a player to play on in order to prove that an opponent's group is dead, since playing in their own territory to do this would reduce their score. Therefore, the game is divided into a phase of ordinary play, and a phase of determination of life and death (which according to the Japanese rules is not technically part of the game).

Compensation
To allow players of different skills to compete fairly, handicaps and komi are used. These are considered a part of the game and, unlike in many other games, they do not distort the nature of the game. Players at all levels employ handicaps to make the game more balanced.

Komi
In an "even", or non-handicap game, Black's initial advantage of moving first can be offset by komi (compensation points): a fixed number of points, agreed before the game, added to White's score at the end of the game. The correct value of komi (to properly compensate for Black's advantage) is controversial, but common values are 5.5, 6.5, or 7.5; the fractional value avoids a tied game. In a handicap game, komi is usually set to 0.5 (i.e., White wins if the game is tied). A handicap game with a handicap of 1 starts like an even game, but White receives only 0.5 komi (i.e., a White player who is stronger by one rank is handicapped only by Black's first-move advantage).

Before the 20th century, there was no komi system. When the great Shusaku was once asked how an important game came out, he said simply, "I had Black", implying that victory was inevitable. As more people became aware of the significance of Black having the first move, komi was introduced. The amount of komi has been increased periodically based on analysis of game results indicating >50% wins for Black; each time, after a period of adjustment Black has again begun winning >50% of games. When it was introduced in Japanese Professional games, it was 4.5 points. However, Black still had a better chance to win, so komi was increased to 5.5 points in 1974. In 2002, the Japanese Go Association again increased the komi value to 6.5.

Handicap
Handicaps are given by allowing the weaker player to take Black and declaring White's first few moves as mandatory "pass" moves. In practice, this means that Black's first move is to place a certain number of stones (usually the number is equal to the difference in the players' ranks) on the board before allowing White to play. Traditionally, the hoshi ("star points") – strategically important intersections marked with small dots—are used to place these handicap stones. On the 19 × 19 board, there are nine star points: at the four 4–4 points in the corners, at the four 4–10 points along the sides, and one at the 10–10 point (the centre of the board, or tengen in Japanese). Smaller boards such as the 13 × 13 and 9 × 9 also have star points. The 13 × 13 has 9 at the 4–4 points, 4–7 points, and the center. The 9 × 9 board has only 5 points: the 3–3 points and the center.

When Black is only one rank weaker (also known as one stone weaker, due to the close relationship between ranks and the handicap system), Black is given the advantage of playing Black, perhaps without komi, but without any mandatory White passes. For rank differences from two through nine stones, the appropriate number of handicap stones are used. Beyond nine stones, the difference in strength between the players is usually considered great enough that the game is more a lesson where White teaches Black than a competition. Thus, nine stones is the nominal upper limit on handicap stones regardless of the difference in rank (although higher numbers of stones, up to 41 stones in some cases, may be given if the teacher wants a greater challenge).

Variations
Go was already an ancient game before its rules were codified, and therefore, although the basic rules and strategy are universal, there are regional variations in some aspects of the rules.

Seki
For defining this notion, it is useful to introduce some additional terminology:

 * Terminology
 * An eye is a connected group of one (or more) empty intersections entirely surrounded by a chain or chains of stones of one color.
 * A chain of one color is independently alive if it is (or can be made to be) adjacent to two eyes.

These definitions are given only loosely, since a number of complications arise when attempts are made to formalize the notion of life and death.

A group of stones of one color is said to be alive by seki (or in seki) if it is not independently alive, yet cannot be captured by the opponent.

For example, in the diagram above, the black and white groups each have only one eye. Hence they are not independently alive. However, if either Black or White were to play at the circled point, the other side would then capture their group by playing in its eye. In this case both the black and white groups are alive by seki.

In the diagram above, the circled point is not surrounded by stones of a single color, and accordingly is not counted as territory for either side (irrespective of ruleset). In more complex cases, as here,

a vacant point may be surrounded by a group of a single color which is in seki. According to Japanese and Korean rules, such a point is nonetheless treated as neutral territory for scoring purposes. Generally, the Japanese and Korean rules only count a vacant point as territory for one color if it is surrounded by a group or groups of that color that are independently alive.

Repetition
The major division in rules to prevent repetition is between the simple ko rule and the super ko rule: the simple ko rule (typically part of the Japanese ruleset) prevents repetition of the last previous board position, while the superko rule (typically part of Chinese derived rulesets, including those of the AGA and the New Zealand Go Society) prevents repetition of any previous position. In both cases, the rule does not, however, prohibit passing.

The super ko rule is differentiated into situational super ko (SSK, in which the "position" that cannot be recreated includes knowledge of whose turn it is) and positional super ko (PSK, which ignores whose turn it is). Natural situational super ko (NSSK) is a variant in which what matters is not whose turn it is, but who created the position (i. e., who made the last move other than a pass.)

The Ing rules feature a complicated distinction between "fighting" and "disturbing" ko.

Situations other than ko which could lead to an endlessly repeating position are rare enough that many frequent players never encounter them; their treatment depends on what ruleset is being used. The simple ko rule generally requires the inclusion of additional rules to handle other undesirable repetitions (e.g. long cycles which can lead to no result where the game must be replayed).

The first position below is an example of a triple ko, taken, with minor changes, from Ikeda Toshio's On the Rules of Go.

Without a superko rule, this position would lead to an endless cycle, and hence "no result", a draw, or some other outcome determined by the rules.

For simplicity, when discussing this position using the superko rule, it is assumed that the last move placed a stone in a position unoccupied since the beginning of the game, and away from the ko. Under positional and situational super ko, Black captures the white group. This is also the case with natural situational super ko if it is Black's turn. If it is White's turn however, then NSSK exhibits odd behavior. White can get a seki by passing, but only at the cost of allowing Black unlimited moves away from the ko. If White insists on saving their group, the final position might look like the second diagram. On the other hand, with the first move (which should be a pass), White wins by two points in the third position using NSSK (assuming area scoring). Black's best response, in terms of maximizing their score, is a pass.

Suicide
Currently, most major rulesets forbid playing such that a play results in that player's own stones being removed from the board. Some rulesets (notably, New Zealand derived rules and Ing rules) allow suicide of more than one stone. Suicide of more than one stone rarely occurs in real games, but in certain circumstances, a suicidal move may threaten the opponent's eye shape, yielding a ko threat.

Compensation
The major rulesets differ in how handicap stones are placed on the board: free placement (Chinese), where stones can be placed anywhere (as if the player's turn repeated); and fixed placement (Japanese), where tradition dictates the stone placement (according to the handicap). Area scoring rules and territory scoring rules also differ in the compensation given for each handicap stone (since each handicap stone would count under area scoring). Komi (compensation for going first) also varies, ranging from several fixed values (commonly 5.5, 6.5, or 7.5) to various meta-games to determine a value (notably Auction Komi).

Board sizes
Most Go is played on a 19 × 19 board, but 13 × 13 and 9 × 9 are also popular sizes. Historically other board sizes were commonly used (notably 17 × 17, a predecessor of the 19 × 19 board in ancient China). Go is also sometimes played on various novelty sized boards as small as 5 × 5 and larger than 19 × 19. All board sizes have an odd number of lines to ensure that there is a center point, possibly to make mirror Go a less attractive strategy. Generally all rules apply to all board sizes, with the exception of handicaps and compensation (whose placement and values vary according to board size).

Scoring
Historically in China a scoring system was used that penalized the player who had the greatest number of unconnected live groups of stones. On the basis that every group needs two eyes to be alive, and that the two eyes could not be filled in, two points were deducted from the score for each live group at the end of the game. This was known as the "cutting penalty" in Chinese, and is sometimes referred to as the "group tax" in English. This rule is not applied in modern Chinese scoring.

Issues
In general, there are three closely related issues which have to be addressed by each variation of the rules.

First, how to ensure that the game comes to an end. Players must be able to settle unsettled situations rather than going around in circles. And neither player should be able to drag the game out indefinitely either to avoid losing or to irritate the other player. Possible methods include: the super-ko rule, time control, or placing an upper bound on the number of moves. This is also affected by the scoring method used since territory scoring penalizes extended play after the boundaries of the territories have been settled.

Second, how to decide which player won the game; and whether draws (jigo) should be allowed. Possible terms to include in the score are: komi, prisoners captured during the game, stones in dead groups on the board at the end of the game, points of territory controlled by a player but not occupied by their stones, their living stones, the number of passes, and the number of disjoint living groups on the board.

Third, how to determine whether a group of stones is alive or dead at the end of the game, and whether protective plays are necessary; e.g., connecting a group which could be captured if all neutral territory were filled. If the players are unable to agree, some rules provide for arbitration using virtual attempts to capture the group. Others allow play to resume until the group is captured or clearly immortal.

Rulesets
There are many official rulesets for playing Go. These vary in significant ways, such as the method used to count the final score, and in very small ways, such as whether the two kinds of "bent four in the corner" positions result in removal of the dead stones automatically at the end of the game or whether the position must be played out, and whether the players must start the game with a fixed number of stones or with an unbounded number.

Rulesets include Japanese, Chinese, Korean, the American Go Association, Ing, and New Zealand.

Japanese rules
These are rules used in Japan and, with some minor differences, in Korea. They are in wide use throughout the West, sometimes known as "territory" rules. The scoring is based on territory and captured stones. At the end of the game, prisoners are placed in the opponent's territory and players rearrange the board so that territories are easy to count, leaving a visual image resembling the game, which some players find aesthetically pleasing. There is no superko (the triple ko leads to an undecided game). Suicide is always forbidden. Komi is 6.5.

Disagreements about whether certain groups are alive or dead, and about the counting of territory, are resolved in a notoriously complex manner (see above).

Japanese rules count vacant points in a seki as neutral, even if they are entirely surrounded by stones of a single color.

World Amateur Go Championship Rules
The rules of the World Amateur Go Championship are based on the Japanese rules, with some differences. These rules are sanctioned by the International Go Federation.

Chinese rules
This is the other major set of rules in widespread use, also known as "area" rules. At the end, one player (usually Black) fills in all of their captured territory, and the other (White) stones are removed from the board. Prisoners do not count. Black stones are then arranged in groups of ten—eighteen such groups, plus half the komi, plus at least one additional stone = victory for Black. So for example with a komi of 7.5 points, under Chinese rules Black needs at least 184.5 (but usually 185 since half points are not that common) stones on the board at the end to win. Komi is usually 7.5 points.

In the Chinese rules, there is no penalty for playing within one's territory at the end of the game, for example to kill and remove dead enemy groups. Thus passing to signal that one believes that there are no more useful moves may be conceived as simply being a convenient device to accelerate the end of the game – assuming one is not mistaken. The result will always be the same as if the game had been played out entirely.

The fact that disagreements can be resolved by playing on means that Chinese-style rules can be implemented easily without the need for the rules to define what is meant by "living" and "dead" groups.

World Mind Sports Games Rules
The rules of the First World Mind Sports Games, held in Beijing in October 2008, are based on the Chinese rules, but are simpler, and represent a compromise with the Japanese and Korean rules. These rules are sanctioned by the International Go Federation.

These rules use area scoring, and have a komi of 6.5. Black has one further point deducted in the event that White was the first player to pass in the game. This last feature is a compromise with Japanese and Korean rules in that it is similar, in terms of its strategic consequences, to territory scoring. Unlike the Chinese rules, this rule will generally impose a penalty for an additional move at the end of the game within one's territory. In particular, the result of the game may differ by up to a point from what it would have been had both players played it out.

The game normally ends after two consecutive passes, but in the event of disagreement about the score, play resumes in the original order. Once this resumption has occurred, then when two consecutive passes do eventually occur again, play stops and all stones left on the board are deemed alive. Thus after a single disagreement, the players are required to play the game out entirely. (By this point in the game, there is no longer any penalty for making "useless" plays within one's territory to kill dead enemy groups, since the one-point advantage for passing first has already been attributed to one player or the other by the first set of consecutive passes.)

Suicide is forbidden in these rules. Unlike the Japanese rules, the WMSG rules apply superko (specifically, positional superko).

AGA rules
These are used by the American Go Association. Some special rules (like giving the opponent a prisoner when passing) are added, which make the area scoring and territory scoring equal.

The Federation Française de Go also uses AGA rules. The British Go Association also adopted the AGA rules, with some minor departures, in April 2008.

Ing rules
The scoring is basically the same as area scoring, but is done with a special technique involving "Ing bowls". Both players must start with exactly 180 stones; the Ing Foundation makes special bowls that allow players to count their stones easily. Prisoners come back to the owner. After the game finishes, both players fill their empty territory with their stones. The one that gets rid of all of them is the winner. Black pays White eight points (komi) by allowing four white stones in Black's territory to be placed at the beginning of the counting phase. As Black wins ties it is 7.5 in effect. The ko rule makes a distinction between "fighting" and "disturbing" ko. Multi-stone suicide is allowed. This ruleset was invented and promoted by Ing Chang-ki.

New Zealand rules
Area scoring is used. Multi-stone suicide is allowed. A stone may not be played such that the resulting board position repeats the whole board position as it was after any of that player's previous moves. (Some people call this a "superko" rule.) Komi is 7 points (so draws with equal scores are possible).

Differences
In most cases the differences between the rulesets are negligible. The choice of ruleset rarely results in a difference in score of more than one point, and the strategy and tactics of the game are mostly unaffected by the ruleset used. Differences come from passing moves (if white and black did not pass the same number of times) and from seki scoring.

title: Rules of Go