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ICANN

The Internet Corporation for Assigned Names and Numbers (ICANN ) is a global multistakeholder group and nonprofit organization headquartered in the United States responsible for coordinating the maintenance and procedures of several databases related to the namespaces and numerical spaces of the Internet, ensuring the Internet's stable and secure operation. ICANN performs the actual technical maintenance work of the Central Internet Address pools and DNS root zone registries pursuant to the Internet Assigned Numbers Authority (IANA) function contract. The contract regarding the IANA stewardship functions between ICANN and the National Telecommunications and Information Administration (NTIA) of the United States Department of Commerce ended on October 1, 2016, formally transitioning the functions to the global multistakeholder community.

Much of its work has concerned the Internet's global Domain Name System (DNS), including policy development for internationalization of the DNS, introduction of new generic top-level domains (TLDs), and the operation of root name servers. The numbering facilities ICANN manages include the Internet Protocol address spaces for IPv4 and IPv6, and the assignment of address blocks to regional Internet registries. ICANN also maintains registries of Internet Protocol identifiers.

ICANN's primary principles of operation have been described as helping preserve the operational stability of the Internet; promoting competition; achieving broad representation of the global Internet community; and developing policies appropriate to its mission through bottom-up, consensus-based processes. The organization has often included a motto of "One World. One Internet." on annual reports beginning in 2010, on less formal publications, as well as their official website.

ICANN was officially incorporated in the state of California on September 30, 1998. Originally headquartered in Marina del Rey in the same building as the University of Southern California's Information Sciences Institute (ISI), its offices are now in the Playa Vista neighborhood of Los Angeles.

History
Before the establishment of ICANN, the IANA function of administering registries of Internet protocol identifiers (including the distributing top-level domains and IP addresses) was performed by Jon Postel, a computer science researcher who had been involved in the creation of ARPANET, first at UCLA and then at USC-ISI. In 1997 Postel testified before Congress that this had come about as a "side task" to this research work. The Information Sciences Institute was funded by the U.S. Department of Defense, as was SRI International's Network Information Center, which also performed some assigned name functions.

As the Internet grew and expanded globally, the U.S. Department of Commerce initiated a process to establish a new organization to perform the IANA functions. On January 30, 1998, the National Telecommunications and Information Administration (NTIA), an agency of the U.S. Department of Commerce, issued for comment, "A Proposal to Improve the Technical Management of Internet Names and Addresses." The proposed rule making, or "Green Paper", was published in the Federal Register on February 20, 1998, providing opportunity for public comment. NTIA received more than 650 comments as of March 23, 1998, when the comment period closed.

The Green Paper proposed certain actions designed to privatize the management of Internet names and addresses in a manner that allows for the development of competition and facilitates global participation in Internet management. The Green Paper proposed for discussion a variety of issues relating to DNS management including private sector creation of a new not-for-profit corporation (the "new corporation") managed by a globally and functionally representative board of directors. ICANN was formed in response to this policy. ICANN managed the Internet Assigned Numbers Authority (IANA) under contract to the United States Department of Commerce (DOC) and pursuant to an agreement with the IETF.

ICANN was incorporated in California on September 30, 1998, with entrepreneur and philanthropist Esther Dyson as founding chairwoman. It is a nonprofit public benefit corporation "organized under the California Nonprofit Public Benefit Corporation Law for charitable and public purposes." ICANN was established in California due to the presence of Jon Postel, who was a founder of ICANN and was set to be its first Chief Technology Officer prior to his unexpected death. ICANN formerly operated from the same Marina del Rey building where Postel formerly worked, which is home to an office of the Information Sciences Institute at the University of Southern California. However, ICANN's headquarters is now located in the nearby Playa Vista neighborhood of Los Angeles.

Per its original by-laws, primary responsibility for policy formation in ICANN was to be delegated to three supporting organizations (Address Supporting Organization, Domain Name Supporting Organization, and Protocol Supporting Organization), each of which was to develop and recommend substantive policies and procedures for the management of the identifiers within their respective scope. They were also required to be financially independent from ICANN. As expected, the regional Internet registries and the IETF agreed to serve as the Address Supporting Organization and Protocol Supporting Organization respectively, and ICANN issued a call for interested parties to propose the structure and composition of the Domain Name Supporting Organization. In March 1999, the ICANN Board, based in part on the DNSO proposals received, decided instead on an alternate construction for the DNSO which delineated specific constituencies bodies within ICANN itself, thus adding primary responsibility for DNS policy development to ICANN's existing duties of oversight and coordination.

On July 26, 2006, the United States government renewed the contract with ICANN for performance of the IANA function for an additional one to five years. The context of ICANN's relationship with the U.S. government was clarified on September 29, 2006, when ICANN signed a new memorandum of understanding with the United States Department of Commerce (DOC). This document gave the DOC oversight over some of the ICANN operations.

In July 2008, the DOC reiterated an earlier statement that it has "no plans to transition management of the authoritative root zone file to ICANN". The letter also stresses the separate roles of the IANA and VeriSign.

On September 30, 2009, ICANN signed an agreement with the DOC (known as the "Affirmation of Commitments") that confirmed ICANN's commitment to a multistakeholder governance model, but did not remove it from DOC oversight and control. The Affirmation of Commitments, which aimed to create international oversight, ran into criticism.

On March 10, 2016, ICANN and the DOC signed a historic, culminating agreement to finally remove ICANN and IANA from the control and oversight of the DOC. On October 1, 2016, ICANN was freed from U.S. government oversight.

Since its creation, ICANN has been the subject of criticism and controversy. In 2000, professor Michael Froomkin of the University of Miami School of Law argued that ICANN's relationship with the U.S. Department of Commerce is illegal, in violation of either the Constitution or federal statutes. On June 10, 2024, it was announced that Kurt Erik Lindqvist, who has been CEO of the London Internet Exchange since 2019, was to become the new president and CEO of ICANN on December 5, 2024.

Notable events
On March 18, 2002, publicly elected At-Large Representative for North America board member Karl Auerbach sued ICANN in the Superior Court of Los Angeles County, California, to gain access to ICANN's accounting records without restriction. Judge Dzintra Janavs ruled in Auerbach's favor on July 29, 2002.

During September and October 2003, ICANN played a crucial role in the conflict over VeriSign's "wild card" DNS service Site Finder. After an open letter from ICANN issuing an ultimatum to VeriSign, later endorsed by the Internet Architecture Board, the company voluntarily ended the service on October 4, 2003. After this action, VeriSign filed a lawsuit against ICANN on February 27, 2004, claiming that ICANN had exceeded its authority. By this lawsuit, VeriSign sought to reduce ambiguity about ICANN's authority. The antitrust component of VeriSign's claim was dismissed during August 2004. VeriSign's challenge that ICANN overstepped its contractual rights is currently outstanding. A proposed settlement already approved by ICANN's board would resolve VeriSign's challenge to ICANN in exchange for the right to increase pricing on .com domains. At the meeting of ICANN in Rome, which took place from March 2 to 6, 2004, ICANN agreed to ask approval of the U.S. Department of Commerce for the Waiting List Service of VeriSign.

On May 17, 2004, ICANN published a proposed budget for the year 2004–05. It included proposals to increase the openness and professionalism of its operations, and increased its proposed spending from US$8.27 million to $15.83 million. The increase was to be funded by the introduction of new top-level domains, charges to domain registries, and a fee for some domain name registrations, renewals and transfers (initially US$0.20 for all domains within a country-code top-level domain, and US$0.25 for all others). The Council of European National Top Level Domain Registries (CENTR), which represents the Internet registries of 39 countries, rejected the increase, accusing ICANN of a lack of financial prudence and criticizing what it describes as ICANN's "unrealistic political and operational targets". Despite the criticism, the registry agreement for the top-level domains jobs and travel includes a US$2 fee on every domain the licensed companies sell or renew.

After a second round of negotiations during 2004, the TLDs eu, asia, travel, jobs, mobi, and cat were introduced during 2005.

On February 28, 2006, ICANN's board approved a settlement with VeriSign in the lawsuit resulting from SiteFinder that involved allowing VeriSign (the registry) to raise its registration fees by up to 7% a year. This was criticised by a few members of the U.S. House of Representatives' Small Business Committee.

During February 2007, ICANN began procedures to end accreditation of one of their registrars, RegisterFly amid charges and lawsuits involving fraud, and criticism of ICANN's management of the situation. ICANN has been the subject of criticism as a result of its handling of RegisterFly, and the harm caused to thousands of clients as a result of what has been termed ICANN's "laissez faire attitude toward customer allegations of fraud".

On May 23, 2008, ICANN issued enforcement notices against ten accredited registrars and announced this through a press release entitled "'Worst Spam Offenders' Notified by ICANN, Compliance system working to correct Whois and other issues." This was largely in response to a report issued by KnujOn, called "The 10 Worst Registrars" in terms of spam advertised junk product sites and compliance failure. The mention of the word "spam" in the title of the ICANN memo is somewhat misleading since ICANN does not address issues of spam or email abuse. Website content and usage are not within ICANN's mandate. However, the KnujOn report details how various registrars have not complied with their contractual obligations under the Registrar Accreditation Agreement (RAA). The main point of the KnujOn research was to demonstrate the relationships between compliance failure, illicit product traffic, and spam. The report demonstrated that out of 900 ICANN accredited registrars, fewer than 20 held 90% of the web domains advertised in spam. These same registrars were also most frequently cited by KnujOn as failing to resolve complaints made through the Whois Data Problem Reporting System (WDPRS).

On June 26, 2008, the ICANN Board started a new process of TLD naming policy to take a "significant step forward on the introduction of new generic top-level domains." This program envisioned the availability of many new or already proposed domains, as well a new application and implementation process.

On October 1, 2008, ICANN issued breach notices against Joker and Beijing Innovative Linkage Technology Ltd. after further researching reports and complaints issued by KnujOn. These notices gave the registrars 15 days to fix their Whois investigation efforts.

In 2010, ICANN approved a major review of its policies with respect to accountability, transparency, and public participation by the Berkman Center for Internet and Society at Harvard University. This external review was an assistance of the work of ICANN's Accountability and Transparency Review team.

On February 3, 2011, ICANN announced that it had distributed the last batch of its remaining IPv4 addresses to the world's five regional Internet registries, the organizations that manage IP addresses in different regions. These registries began assigning the final IPv4 addresses within their regions until they ran out completely.

On June 20, 2011, the ICANN board voted to end most restrictions on the names of generic top-level domains (gTLD). Companies and organizations became able to choose essentially arbitrary top-level Internet domain names. The use of non-Latin characters (such as Cyrillic, Arabic, Chinese, etc.) is also allowed in gTLDs. ICANN began accepting applications for new gTLDS on January 12, 2012. The initial price to apply for a new gTLD was set at $185,000 and the annual renewal fee is $25,000.

During December 2011, the Federal Trade Commission stated ICANN had long failed to provide safeguards that protect consumers from online swindlers.

Following the 2013 NSA spying scandal, ICANN endorsed the Montevideo Statement, although no direct connection between these could be proven.

On October 1, 2016, ICANN ended its contract with the United States Department of Commerce National Telecommunications and Information Administration ( NTIA ) and entered the private sector.

The European Union's General Data Protection Regulation (active since May 25, 2018) impacted on ICANN operations, which the latter tried to fix through last-minute changes.

Structure
From its founding to the present, ICANN has been formally organized as a nonprofit corporation "for charitable and public purposes" under the California Nonprofit Public Benefit Corporation Law. It is managed by a 16-member board of directors composed of eight members selected by a nominating committee on which all the constituencies of ICANN are represented; six representatives of its Supporting Organizations, sub-groups that deal with specific sections of the policies under ICANN's purview; an at-large seat filled by an at-large organization; and the president / CEO, appointed by the board.

There are currently three supporting organizations: the Generic Names Supporting Organization (GNSO) deals with policy making on generic top-level domains (gTLDs); the Country Code Names Supporting Organization (ccNSO) deals with policy making on country-code top-level domains (ccTLDs); the Address Supporting Organization (ASO) deals with policy making on IP addresses.

ICANN also relies on some advisory committees and other advisory mechanisms to receive advice on the interests and needs of stakeholders that do not directly participate in the Supporting Organizations. These include the Governmental Advisory Committee (GAC), which is composed of representatives of a large number of national governments from all over the world; the At-Large Advisory Committee (ALAC), which is composed of individual Internet users from around the world selected by each of the Regional At-Large Organizations (RALO) and Nominating Committee; the Root Server System Advisory Committee, which provides advice on the operation of the DNS root server system; the Security and Stability Advisory Committee (SSAC), which is composed of Internet experts who study security issues pertaining to ICANN's mandate; and the Technical Liaison Group (TLG), which is composed of representatives of other international technical organizations that focus, at least in part, on the Internet.

Representatives
The Governmental Advisory Committee has representatives from 179 states and 38 Observer organizations, including the Holy See, Cook Islands, Niue, Taiwan, Hong Kong, Bermuda, Montserrat, the European Commission and the African Union Commission.

Observers
In addition the following organizations are GAC Observers:

 * African Telecommunications Union
 * Asia-Pacific Telecommunity
 * Caribbean Telecommunications Union (CTU)
 * Commonwealth Telecommunications Organisation (CTO)
 * Council of Europe
 * Economic Commission for Africa (ECA)
 * European Broadcasting Union
 * European Organization for Nuclear Research (CERN)
 * European Space Agency
 * International Labour Office
 * International Telecommunication Union (ITU)
 * International Criminal Police Organization (INTERPOL)
 * International Red Cross and Red Crescent Movement
 * Latin American Association of Telecom Regulatory Agencies (REGULATEL)
 * League of Arab States
 * New Partnership for Africa's Development (NEPAD)
 * Organisation for Economic Co-operation and Development
 * The Organization for Islamic Cooperation
 * Organization of American States
 * Organisation internationale de la Francophonie (OIF)
 * Pacific Islands Forum
 * Secretariat of the Pacific Community (SPC)
 * Inter-American Telecommunication Commission (CITEL)
 * International Criminal Court
 * United Nations Educational Scientific and Cultural Organization (UNESCO)
 * Universal Postal Union
 * World Bank
 * World Health Organization (WHO)
 * World Intellectual Property Organization (WIPO)
 * World Meteorological Organization
 * World Trade Organization

Trusted Community Representatives
As the operator of the IANA domain name functions, ICANN is responsible for the DNSSEC management of the root zone. While day-to-day operations are managed by ICANN and Verisign, the trust is rooted in a group of Trusted Community Representatives. The members of this group must not be affiliated with ICANN, but are instead members of the broader DNS community, volunteering to become a Trusted Community Representative. The role of the representatives are primarily to take part in regular key ceremonies at a physical location, organized by ICANN, and to safeguard the key materials in between.

Democratic input
In the Memorandum of understanding that set up the relationship between ICANN and the U.S. government, ICANN was given a mandate requiring that it operate "in a bottom-up, consensus-driven, democratic manner." However, the attempts that ICANN has made to establish an organizational structure that would allow wide input from the global Internet community did not produce results amenable to the current Board. As a result, the At-Large constituency and direct election of board members by the global Internet community were soon abandoned.

ICANN holds periodic public meetings rotated between continents for the purpose of encouraging global participation in its processes. Resolutions of the ICANN Board, preliminary reports, and minutes of the meetings are published on the ICANN website, sometimes in real-time. However, there are criticisms from ICANN constituencies including the Noncommercial Users Constituency (NCUC) and the At-Large Advisory Committee (ALAC) that there is not enough public disclosure and that too many discussions and decisions take place out of sight of the public.

During the early 2000s, there had been speculation that the United Nations might assume control of ICANN, followed by a negative reaction from the U.S. government and worries about a division of the Internet. The World Summit on the Information Society in Tunisia in November 2005 agreed not to get involved in the day-to-day and technical operations of ICANN. However it also agreed to establish an international Internet Governance Forum, with a consultative role on the future governance of the Internet. ICANN's Government Advisory Committee is currently established to provide advice to ICANN regarding public policy issues and has participation by many of the world's governments.

Some have attempted to argue that ICANN was never given the authority to decide policy, e.g., choose new TLDs or exclude other interested parties who refuse to pay ICANN's US$185,000 fee but was to be a technical caretaker. Critics suggest that ICANN should not be allowed to impose business rules on market participants and that all TLDs should be added on a first-come, first-served basis and the market should be the arbiter of who succeeds and who does not.

Uniform Domain-Name Dispute Resolution Policy (UDRP)
One task that ICANN was asked to do was to address the issue of domain name ownership resolution for generic top-level domains (gTLDs). ICANN's attempt at such a policy was drafted in close cooperation with the World Intellectual Property Organization (WIPO), and the result has now become known as the Uniform Dispute Resolution Policy (UDRP). This policy essentially attempts to provide a mechanism for rapid, cheap and reasonable resolution of domain name conflicts, avoiding the traditional court system for disputes by allowing cases to be brought to one of a set of bodies that arbitrate domain name disputes. According to ICANN policy, domain registrants must agree to be bound by the UDRP—they cannot get a domain name without agreeing to this.

Examination of the UDRP decision patterns has caused some to conclude that compulsory domain name arbitration is less likely to give a fair hearing to domain name owners asserting defenses under the First Amendment and other laws, compared to the federal courts of appeal in particular.

Proposed elimination of public DNS whois
In 2013, the initial report of ICANN's Expert Working Group has recommended that the present form of Whois, a utility that allows anyone to know who has registered a domain name on the Internet, should be "abandoned". It recommends it be replaced with a system that keeps most registration information secret (or "gated") from most Internet users, and only discloses information for "permissible purposes". ICANN's list of permissible purposes includes domain name research, domain name sale and purchase, regulatory enforcement, personal data protection, legal actions, and abuse mitigation. Whois has been a key tool of investigative journalists interested in determining who was disseminating information on the Internet. The use of whois by journalists is not included in the list of permissible purposes in the initial report.

Proposals for reform
Proposals have been made to internationalize ICANN's monitoring responsibilities (currently the responsibility of the US), to transform it into an international organization (under international law), and to "establish an intergovernmental mechanism enabling governments, on an equal footing, to carry out their role and responsibilities in international public policy issues pertaining to the Internet".

IBSA proposal (2011)
One controversial proposal, resulting from a September 2011 summit between India, Brazil, and South Africa (IBSA), would seek to move Internet governance into a "UN Committee on Internet-Related Policy" (UN-CIRP). The action was a reaction to a perception that the principles of the 2005 Tunis Agenda for the Information Society have not been met. The statement proposed the creation of a new political organization operating as a component of the United Nations to provide policy recommendations for the consideration of technical organizations such as ICANN and international bodies such as the ITU. Subsequent to public criticisms, the Indian government backed away from the proposal.

Montevideo Statement on the Future of Internet Cooperation (2013)
On October 7, 2013, the Montevideo Statement on the Future of Internet Cooperation was released by the managers of a number of organizations involved in coordinating the Internet's global technical infrastructure, loosely known as the "I*" (or "I-star") group. Among other things, the statement "expressed strong concern over the undermining of the trust and confidence of Internet users globally due to recent revelations of pervasive monitoring and surveillance" and "called for accelerating the globalization of ICANN and IANA functions, towards an environment in which all stakeholders, including all governments, participate on an equal footing". This desire to reduce United States association with the internet is considered a reaction to the ongoing NSA surveillance scandal. The statement was signed by the managers of the Internet Corporation for Assigned Names and Numbers (ICANN), the Internet Engineering Task Force, the Internet Architecture Board, the World Wide Web Consortium, the Internet Society, and the five regional Internet address registries (African Network Information Center, American Registry for Internet Numbers, Asia-Pacific Network Information Centre, Latin America and Caribbean Internet Addresses Registry, and Réseaux IP Européens Network Coordination Centre).

Global Multistakeholder Meeting on the Future of Internet Governance (2013)
During October 2013, Fadi Chehadé, former president and CEO of ICANN, met with Brazilian president Dilma Rousseff in Brasilia. Upon Chehadé's invitation, the two announced that Brazil would host an international summit on Internet governance during April 2014. The announcement came after the 2013 disclosures of mass surveillance by the U.S. government, and Rousseff's speech at the opening session of the 2013 United Nations General Assembly, where she strongly criticized the American surveillance program as a "breach of international law". The "Global Multistakeholder Meeting on the Future of Internet Governance (NET mundial)" will include representatives of government, industry, civil society, and academia. At the IGF VIII meeting in Bali in October 2013 a commenter noted that Brazil intends the meeting to be a "summit" in the sense that it will be high level with decision-making authority. The organizers of the "NET mundial" meeting have decided that an online forum called "/1net", set up by the I* group, will be a major conduit of non-governmental input into the three committees preparing for the meeting in April.

The Obama administration that had joined critics of ICANN during 2011 announced in March 2014 that they intended to transition away from oversight of the IANA functions contract. The current contract that the United States Department of Commerce has with ICANN expired in 2015, in its place the NTIA will transition oversight of the IANA functions to the 'global multistakeholder community'.

NetMundial Initiative (2014)
The NetMundial Initiative is a plan for international governance of the Internet that was first proposed at the Global Multistakeholder Meeting on the Future of Internet Governance (GMMFIG) conference (April 23–24, 2014) and later developed into the NetMundial Initiative by ICANN CEO Fadi Chehadé along with representatives of the World Economic Forum (WEF) and the Brazilian Internet Steering Committee (Comitê Gestor da Internet no Brasil), commonly referred to as "CGI.br".

The meeting produced a nonbinding statement in favor of consensus-based decision-making. It represented a compromise and did not harshly condemn mass surveillance or support net neutrality, despite initial endorsement for that from Brazil. The final resolution says ICANN should be controlled internationally by September 2015. A minority of governments, including Russia, China, Iran and India, were unhappy with the final resolution and wanted multilateral management for the Internet, rather than broader multistakeholder management.

A month later, the Panel on Global Internet Cooperation and Governance Mechanisms (convened by the Internet Corporation for Assigned Names and Numbers (ICANN) and the World Economic Forum (WEF) with assistance from The Annenberg Foundation), endorsed and included the NetMundial statement in its own report.

During June 2014, France strongly attacked ICANN, saying ICANN is not a fit venue for Internet governance and that alternatives should be sought.

TLD expansion and concerns about specific top-level domains
During 2011, seventy-nine companies, including The Coca-Cola Company, Hewlett-Packard, Samsung and others, signed a petition against ICANN's new TLD program (sometimes referred to as a "commercial landgrab" ), in a group organized by the Association of National Advertisers. As of September 2014, this group, the Coalition for Responsible Internet Domain Oversight, that opposes the rollout of ICANN's TLD expansion program, has been joined by 102 associations and 79 major companies. Partly as a response to this criticism, ICANN initiated an effort to protect trademarks in domain name registrations, which eventually culminated in the establishment of the Trademark Clearinghouse.

.sucks domain
ICANN has received more than $60 million from gTLD auctions, and has accepted the controversial domain name ".sucks" (referring to the primarily US slang for being inferior or objectionable). sucks domains are owned and controlled by the Vox Populi Registry which won the rights for .sucks gTLD in November 2014.

The .sucks domain registrar has been described as "predatory, exploitive and coercive" by the Intellectual Property Constituency that advises the ICANN board. When the .sucks registry announced their pricing model, "most brand owners were upset and felt like they were being penalized by having to pay more to protect their brands." Because of the low utility of the ".sucks" domain, most fees come from "Brand Protection" customers registering their trademarks to prevent domains being registered.

Canadian brands had complained that they were being charged "exorbitant" prices to register their trademarks as premium names. FTC chair Edith Ramirez has written to ICANN to say the agency will take action against the .sucks owner if "we have reason to believe an entity has engaged in deceptive or unfair practices in violation of Section 5 of the FTC Act". The Register reported that intellectual property lawyers are infuriated that "the dot-sucks registry was charging trademark holders $2,500 for .sucks domains and everyone else $10."

U.S. Representative Bob Goodlatte has said that trademark holders are "being shaken down" by the registry's fees. Jay Rockefeller says that .sucks is "a predatory shakedown scheme" and "Approving '.sucks', a gTLD with little or no public interest value, will have the effect of undermining the credibility ICANN has slowly been building with skeptical stakeholders."

.islam, .halal top level domains
In a long-running dispute, ICANN has so far declined to allow a Turkish company to purchase the .islam and .halal gTLDs, after the Organisation of Islamic Cooperation objected that the gTLDs should be administered by an organization that represents all the world's 1.6 billion Muslims. After a number of attempts to resolve the issue the domains are still held "on hold".

.org price cap removal
In April 2019, ICANN proposed an end to the price cap of org domains and effectively removed it in July in spite of having received 3,252 opposing comments and only six in favor. A few months later, the owner of the domain, the Public Interest Registry, proposed to sell the domain to investment firm Ethos Capital.

.amazon gTLD dispute
In May 2019, ICANN decided in favor of granting exclusive administration rights to amazon.com for the .amazon gTLD after a 7 year long dispute with the Amazon Cooperation Treaty Organization (ACTO).

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Iterative method

In computational mathematics, an iterative method is a mathematical procedure that uses an initial value to generate a sequence of improving approximate solutions for a class of problems, in which the n-th approximation is derived from the previous ones.

A specific implementation with termination criteria for a given iterative method like gradient descent, hill climbing, Newton's method, or quasi-Newton methods like BFGS, is an algorithm of the iterative method. An iterative method is called convergent if the corresponding sequence converges for given initial approximations. A mathematically rigorous convergence analysis of an iterative method is usually performed; however, heuristic-based iterative methods are also common.

In contrast, direct methods attempt to solve the problem by a finite sequence of operations. In the absence of rounding errors, direct methods would deliver an exact solution (for example, solving a linear system of equations $$A\mathbf{x}=\mathbf{b}$$ by Gaussian elimination). Iterative methods are often the only choice for nonlinear equations. However, iterative methods are often useful even for linear problems involving many variables (sometimes on the order of millions), where direct methods would be prohibitively expensive (and in some cases impossible) even with the best available computing power.

Attractive fixed points
If an equation can be put into the form f(x) = x, and a solution x is an attractive fixed point of the function f, then one may begin with a point x1 in the basin of attraction of x, and let xn+1 = f(xn) for n ≥ 1, and the sequence {xn}n ≥ 1 will converge to the solution x. Here xn is the nth approximation or iteration of x and xn+1 is the next or n + 1 iteration of x. Alternately, superscripts in parentheses are often used in numerical methods, so as not to interfere with subscripts with other meanings. (For example, x(n+1) = f(x(n)).) If the function f is continuously differentiable, a sufficient condition for convergence is that the spectral radius of the derivative is strictly bounded by one in a neighborhood of the fixed point. If this condition holds at the fixed point, then a sufficiently small neighborhood (basin of attraction) must exist.

Linear systems
In the case of a system of linear equations, the two main classes of iterative methods are the stationary iterative methods, and the more general Krylov subspace methods.

Introduction
Stationary iterative methods solve a linear system with an operator approximating the original one; and based on a measurement of the error in the result (the residual), form a "correction equation" for which this process is repeated. While these methods are simple to derive, implement, and analyze, convergence is only guaranteed for a limited class of matrices.

Definition
An iterative method is defined by

\mathbf{x}^{k+1} := \Psi ( \mathbf{x}^k ) \,, \quad k\geq0 $$ and for a given linear system $$ A\mathbf x= \mathbf b $$ with exact solution $$ \mathbf{x}^* $$ the error by

\mathbf{e}^k := \mathbf{x}^k - \mathbf{x}^* \,, \quad k\geq0\,. $$ An iterative method is called linear if there exists a matrix $$ C \in \R^{n\times n} $$ such that

\mathbf{e}^{k+1} = C \mathbf{e}^k   \quad \forall \, k\geq0 $$ and this matrix is called the iteration matrix. An iterative method with a given iteration matrix $$ C $$ is called convergent if the following holds

\lim_{k\rightarrow \infty} C^k=0\,. $$

An important theorem states that for a given iterative method and its iteration matrix $$ C $$ it is convergent if and only if its spectral radius $$ \rho(C) $$ is smaller than unity, that is,

\rho(C) < 1 \,. $$

The basic iterative methods work by splitting the matrix $$ A $$ into

A = M - N $$ and here the matrix $$ M $$ should be easily invertible. The iterative methods are now defined as

M \mathbf{x}^{k+1} = N \mathbf{x}^k + b \,, \quad k\geq0\,. $$ From this follows that the iteration matrix is given by

C = I - M^{-1}A = M^{-1}N\,. $$

Examples
Basic examples of stationary iterative methods use a splitting of the matrix $$ A $$ such as

A = D+L+U\,,\quad D := \text{diag}( (a_{ii})_i) $$ where $$ D $$ is only the diagonal part of $$ A $$, and $$ L $$ is the strict lower triangular part of $$ A $$. Respectively, $$ U $$ is the strict upper triangular part of $$ A $$. \quad (\omega \not \in \{0,2\}) $$ Linear stationary iterative methods are also called relaxation methods.
 * Richardson method: $$ M:=\frac{1}{\omega} I \quad (\omega \neq 0) $$
 * Jacobi method: $$ M:=D $$
 * Damped Jacobi method: $$ M:=\frac{1}{\omega}D \quad (\omega \neq 0) $$
 * Gauss–Seidel method: $$ M:=D+L $$
 * Successive over-relaxation method (SOR): $$ M:=\frac{1}{\omega}D+L \quad (\omega \neq 0) $$
 * Symmetric successive over-relaxation (SSOR): $$ M := \frac{1}{\omega (2-\omega)} (D+\omega L) D^{-1} (D+\omega U)

Krylov subspace methods
Krylov subspace methods work by forming a basis of the sequence of successive matrix powers times the initial residual (the Krylov sequence). The approximations to the solution are then formed by minimizing the residual over the subspace formed. The prototypical method in this class is the conjugate gradient method (CG) which assumes that the system matrix $$ A $$ is symmetric positive-definite. For symmetric (and possibly indefinite) $$ A $$ one works with the minimal residual method (MINRES). In the case of non-symmetric matrices, methods such as the generalized minimal residual method (GMRES) and the biconjugate gradient method (BiCG) have been derived.

Convergence of Krylov subspace methods
Since these methods form a basis, it is evident that the method converges in N iterations, where N is the system size. However, in the presence of rounding errors this statement does not hold; moreover, in practice N can be very large, and the iterative process reaches sufficient accuracy already far earlier. The analysis of these methods is hard, depending on a complicated function of the spectrum of the operator.

Preconditioners
The approximating operator that appears in stationary iterative methods can also be incorporated in Krylov subspace methods such as GMRES (alternatively, preconditioned Krylov methods can be considered as accelerations of stationary iterative methods), where they become transformations of the original operator to a presumably better conditioned one. The construction of preconditioners is a large research area.

History
Jamshīd al-Kāshī used iterative methods to calculate the sine of 1° and $\pi$ in The Treatise of Chord and Sine to high precision. An early iterative method for solving a linear system appeared in a letter of Gauss to a student of his. He proposed solving a 4-by-4 system of equations by repeatedly solving the component in which the residual was the largest.

The theory of stationary iterative methods was solidly established with the work of D.M. Young starting in the 1950s. The conjugate gradient method was also invented in the 1950s, with independent developments by Cornelius Lanczos, Magnus Hestenes and Eduard Stiefel, but its nature and applicability were misunderstood at the time. Only in the 1970s was it realized that conjugacy based methods work very well for partial differential equations, especially the elliptic type.

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

title: Iterative method


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International judicial institution

International judicial institutions can be divided into courts, arbitral tribunals and quasi-judicial institutions. Courts are permanent bodies, with near the same composition for each case. Arbitral tribunals, by contrast, are constituted anew for each case. Both courts and arbitral tribunals can make binding decisions. Quasi-judicial institutions, by contrast, make rulings on cases, but these rulings are not in themselves legally binding; the main example is the individual complaints mechanisms available under the various UN human rights treaties.

Institutions can also be divided into global and regional institutions.

The listing below incorporates both currently existing institutions, defunct institutions that no longer exist, institutions which never came into existence due to non-ratification of their constitutive instruments, and institutions which do not yet exist, but for which constitutive instruments have been signed. It does not include mere proposed institutions for which no instrument was ever signed.

International courts

 * International Court of Justice
 * International Tribunal for the Law of the Sea
 * International Criminal Tribunal for the Former Yugoslavia
 * International Criminal Tribunal for Rwanda
 * International Criminal Court
 * International Military Tribunal (Defunct)
 * International Military Tribunal for the Far East (Defunct)
 * International Prize Court (Never established)
 * Permanent Court of International Justice (Defunct. Replaced by the International Court of Justice)

International arbitral tribunals

 * Permanent Court of Arbitration
 * WTO Appellate Body
 * WTO Dispute Settlement Panels
 * NAFTA Dispute Settlement Panels
 * International Centre for the Settlement of Investment Disputes
 * Court of Arbitration for Sport
 * OSCE Court of Conciliation and Arbitration

Quasi-judicial international institutions

 * Human Rights Committee
 * Committee on the Elimination of Racial Discrimination
 * Committee on the Elimination of Discrimination Against Women
 * Committee on Economic, Social and Cultural Rights
 * Committee on the Rights of the Child
 * Committee Against Torture
 * Committee on Migrant Workers
 * Committee on the Rights of Persons with Disabilities

African regional judicial institutions

 * African Court on Human and Peoples' Rights
 * Court of Justice of the African Union (planned)
 * Court of Justice of the Common Market for Eastern and Southern Africa
 * Community Court of Justice of the Economic Community of West African States
 * East African Court of Justice
 * Southern African Development Community Tribunal

Regional judicial institutions of the Americas

 * Inter-American Court of Human Rights
 * Central American Court of Justice
 * Court of Justice of the Andean Community
 * Caribbean Court of Justice
 * Eastern Caribbean Supreme Court

European regional judicial institutions

 * European Court of Justice
 * European General Court
 * European Court of Human Rights
 * Court of Justice of the European Free Trade Agreement States
 * Benelux Court of Justice
 * Economic Court of the Commonwealth of Independent States
 * European Nuclear Energy Tribunal (dormant)
 * Western European Union Tribunal (defunct)
 * European Tribunal in Matters of State Immunity (dormant)

title: International judicial institution


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International Prize Court

The International Prize Court was an international court proposed at the beginning of the 20th century, to hear prize cases. An international agreement to create it, the Convention Relative to the Creation of an International Prize Court, was made at the Second Hague Conference in 1907 but never came into force.

The capturing of prizes (enemy equipment, vehicles, and especially ships) during wartime is a tradition that goes back as far as organized warfare itself. The International Prize Court was to hear appeals from national courts concerning prize cases. Even as a draft, the convention was innovative for the time, in being both the first ever treaty for a truly international court (as opposed to a mere arbitral tribunal), and in providing individuals with access to the court, going against the prevailing doctrines of international law at the time, according to which only states had rights and duties under international law. The convention was opposed, particularly by elements within the United States and the United Kingdom, as a violation of national sovereignty.

The 1907 convention was modified by the Additional Protocol to the Convention Relative to the Creation of an International Prize Court, done at the Hague on October 18, 1910. The protocol was an attempt to resolve some concerns expressed by the United States at the court, which felt it to be in violation of its constitutional provision that provides for the U.S. Supreme Court being the final judicial authority. However, neither the convention nor the subsequent protocol ever entered into force, since only Nicaragua ratified the agreements. As a result, the court never came into existence.

On February 15, 1911, the U.S. Senate ratified the International Prize Court Convention.

A number of ideas from the International Prize Court proposal can be seen in present-day international courts, such as its provision for judges ad hoc, later adopted in the Permanent Court of International Justice and the subsequent International Court of Justice.

title: International Prize Court


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Imam

Imam (, إمام, '; : أئمة, ') is an Islamic leadership position. For Sunni Muslims, Imam is most commonly used as the title of a prayer leader of a mosque. In this context, imams may lead Islamic prayers, serve as community leaders, and provide religious guidance. Thus for Sunnis, anyone can study the basic Islamic sciences and become an Imam.

For most Shia Muslims, the Imams are absolute infallible leaders of the Islamic community after the Prophet. Shias consider the term to be only applicable to the members and descendants of the Ahl al-Bayt, the family of the Islamic prophet Muhammad. In Twelver Shīʿīsm there are 14 infallibles, 12 of which are Imams, the final being Imam Mahdi who will return at the end of times. The title was also used by the Zaidi Shia Imams of Yemen, who eventually founded the Mutawakkilite Kingdom of Yemen (1918–1970).

Sunni imams
Sunni Islam does not conceive of the role of imams in the same sense as Shia Islam: an important distinction often overlooked by non-Muslims. In everyday terms, an imam for Sunni Muslims is the person charged with leading formal Islamic prayers (Fard)—even in locations besides the mosque—whenever prayer is performed in a group of two or more. The imam leads the worship and the congregation copies his actions. Friday sermons are most often given by an appointed imam. All mosques have an imam to lead the congregational prayers—even though it may sometimes just be a member from the gathered congregation rather than an officially appointed, salaried person. Women cannot be imams when men are present but are allowed to be when no men are present. An imam should be chosen, according to Hadith, based on his knowledge of the Quran and Sunnah and his moral character.

Title of scholarly authority
Another well-known use of the term is as an honorary title for a recognized religious scholarly authority in Islam. It is especially used for a jurist (faqīh) and often for the founders of the four Sunni madhhabs or schools of jurisprudence (fiqh), as well as an authority on Quranic exegesis (tafsīr), such as Al-Tabari or Ibn Kathir.

It may also refer to the Muhaddithūn or scholars who created the analytical sciences related to Hadith and sometimes refer to the heads of Muhammad's family in their generational times due to their scholarly authority.

The position of imams in Turkey
Imams are appointed by the state to work at mosques and they are required to be graduates of an İmam Hatip high school or have a university degree in theology. This is an official position regulated by the Presidency of Religious Affairs in Turkey and only males are appointed to this position, whilst female officials under the same state organisation work as preachers and Qur'an course tutors, religious services experts, etc. These officials are supposed to belong to the Hanafi school of the Sunni sect.

A central figure in an Islamic movement is also called an imam, like Imam Nawawi in Syria.

Shia imams
In the Shi'a context, an imam is not only presented as the man of God par excellence, but as participating fully in the names, attributes, and acts that theology usually reserves for God alone. Imams have a meaning more central to belief, referring to leaders of the community. Twelver and Ismaili Shi'a believe that these imams are chosen by God to be perfect examples for the faithful and to lead all humanity in all aspects of life. They also believe that all the imams chosen are free from committing any sin, impeccability which is called ismah. These leaders must be followed since they are appointed by God.

Twelver
Here follows a list of the Twelvers Shia imams:

Fatimah, also Fatimah al-Zahraa, daughter of Muhammed (615–632), is also considered infallible but not an Imam. The Shi'a believe that the last Imam, the 12th Imam Mahdi will one day emerge on the Day of Resurrection (Qiyamah).

Ismaili

 * See Imamah (Ismaili doctrine) and List of Ismaili imams for Ismaili imams.

Zaidi

 * See details under Zaidiyyah, Islamic history of Yemen and Imams of Yemen.

Imams as secular rulers
At times, imams have held both secular and religious authority. This was the case in Oman among the Kharijite or Ibadi sects. At times, the imams were elected. At other times the position was inherited, as with the Yaruba dynasty from 1624 and 1742. See List of rulers of Oman, the Rustamid dynasty: 776–909, Nabhani dynasty: 1154–1624, the Yaruba dynasty: 1624–1742, the Al Said: 1744–present for further information. The Imamate of Futa Jallon (1727–1896) was a Fulani state in West Africa where secular power alternated between two lines of hereditary Imams, or almami. In the Zaidi Shiite sect, imams were secular as well as spiritual leaders who held power in Yemen for more than a thousand years. In 897, a Zaidi ruler, al-Hadi ila'l-Haqq Yahya, founded a line of such imams, a theocratic form of government which survived until the second half of the 20th century. (See details under Zaidiyyah, History of Yemen, Imams of Yemen.)

Ruhollah Khomeini is officially referred to as Imam in Iran. Several Iranian places and institutions are named "Imam Khomeini", including a city, an international airport, a hospital, and a university.

title: Imam


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Instrument flight rules

In aviation, instrument flight rules (IFR) is one of two sets of regulations governing all aspects of civil aviation aircraft operations; the other is visual flight rules (VFR).

The U.S. Federal Aviation Administration's (FAA) Instrument Flying Handbook defines IFR as: "Rules and regulations established by the FAA to govern flight under conditions in which flight by outside visual reference is not safe. IFR flight depends upon flying by reference to instruments in the flight deck, and navigation is accomplished by reference to electronic signals." It is also a term used by pilots and controllers to indicate the type of flight plan an aircraft is flying, such as an IFR or VFR flight plan.

Comparison to visual flight rules
It is possible and fairly straightforward, in relatively clear weather conditions, to fly an aircraft solely by reference to outside visual cues, such as the horizon to maintain orientation, nearby buildings and terrain features for navigation, and other aircraft to maintain separation. This is known as operating the aircraft under visual flight rules (VFR), and is the most common mode of operation for small aircraft. However, it is safe to fly VFR only when these outside references can be clearly seen from a sufficient distance. When flying through or above clouds, or in fog, rain, dust or similar low-level weather conditions, these references can be obscured. Thus, cloud ceiling and flight visibility are the most important variables for safe operations during all phases of flight. The minimum weather conditions for ceiling and visibility for VFR flights are defined in FAR Part 91.155, and vary depending on the type of airspace in which the aircraft is operating, and on whether the flight is conducted during daytime or nighttime. However, typical daytime VFR minimums for most airspace is 3 statute miles of flight visibility and a distance from clouds of 500 feet below, 1,000 feet above, and 2,000 feet horizontally. Flight conditions reported as equal to or greater than these VFR minimums are referred to as visual meteorological conditions (VMC).

Any aircraft operating under VFR must have the required equipment on board, as described in FAR Part 91.205 (which includes some instruments necessary for IFR flight). VFR pilots may use cockpit instruments as secondary aids to navigation and orientation, but are not required to; the view outside of the aircraft is the primary source for keeping the aircraft straight and level (orientation), flying to the intended destination (navigation), and avoiding obstacles and hazards (separation).

Visual flight rules are generally simpler than instrument flight rules, and require significantly less training and practice. VFR provides a great degree of freedom, allowing pilots to go where they want, when they want, and allows them a much wider latitude in determining how they get there.

Instrument flight rules
When operation of an aircraft under VFR is not safe, because the visual cues outside the aircraft are obscured by weather, instrument flight rules must be used instead. IFR permits an aircraft to operate in instrument meteorological conditions (IMC), which is essentially any weather condition less than VMC but in which aircraft can still operate safely. Use of instrument flight rules is also required when flying in "Class A" airspace regardless of weather conditions. Class A airspace extends from 18,000 feet above mean sea level to flight level 600 (60,000 feet pressure altitude) above the contiguous 48 United States and overlying the waters within 12 miles thereof. Flight in Class A airspace requires pilots and aircraft to be instrument equipped and rated and to be operating under instrument flight rules (IFR). In many countries commercial airliners and their pilots must operate under IFR as the majority of flights enter Class A airspace. Procedures and training are significantly more complex compared to VFR instruction, as a pilot must demonstrate competency in conducting an entire cross-country flight solely by reference to instruments.

Instrument pilots must carefully evaluate weather, create a detailed flight plan based around specific instrument departure, en route, and arrival procedures, and dispatch the flight.

Separation and clearance
The distance by which an aircraft avoids obstacles or other aircraft is termed separation. The most important concept of IFR flying is that separation is maintained regardless of weather conditions. In controlled airspace, air traffic control (ATC) separates IFR aircraft from obstacles and other aircraft using a flight clearance based on route, time, distance, speed, and altitude. ATC monitors IFR flights on radar, or through aircraft position reports in areas where radar coverage is not available. Aircraft position reports are sent as voice radio transmissions. In the United States, a flight operating under IFR is required to provide position reports unless ATC advises a pilot that the plane is in radar contact. The pilot must resume position reports after ATC advises that radar contact has been lost, or that radar services are terminated.

IFR flights in controlled airspace require an ATC clearance for each part of the flight. A clearance always specifies a clearance limit, which is the farthest the aircraft can fly without a new clearance. In addition, a clearance typically provides a heading or route to follow, altitude, and communication parameters, such as frequencies and transponder codes.

In uncontrolled airspace, ATC clearances are unavailable. In some states a form of separation is provided to certain aircraft in uncontrolled airspace as far as is practical (often known under ICAO as an advisory service in class G airspace), but separation is not mandated nor widely provided.

Despite the protection offered by flight in controlled airspace under IFR, the ultimate responsibility for the safety of the aircraft rests with the pilot in command, who can refuse clearances.

Weather

It is essential to differentiate between flight plan type (VFR or IFR) and weather conditions (VMC or IMC). While current and forecast weather may be a factor in deciding which type of flight plan to file, weather conditions themselves do not affect one's filed flight plan. For example, an IFR flight that encounters visual meteorological conditions (VMC) en route does not automatically change to a VFR flight, and the flight must still follow all IFR procedures regardless of weather conditions. In the US, weather conditions are forecast broadly as VFR, MVFR (marginal visual flight rules), IFR, or LIFR (low instrument flight rules).

The main purpose of IFR is the safe operation of aircraft in instrument meteorological conditions (IMC). The weather is considered to be MVFR or IMC when it does not meet the minimum requirements for visual meteorological conditions (VMC). To operate safely in IMC ("actual instrument conditions"), a pilot controls the aircraft relying on flight instruments and ATC provides separation.

It is important not to confuse IFR with IMC. A significant amount of IFR flying is conducted in visual meteorological conditions (VMC). Anytime a flight is operating in VMC and in a volume of airspace in which VFR traffic can operate, the crew is responsible for seeing and avoiding VFR traffic; however, because the flight is conducted under instrument flight rules, ATC still provides separation services from other IFR traffic, and can in many cases also advise the crew of the location of VFR traffic near the flight path.

Although dangerous and illegal, a certain amount of VFR flying is conducted in IMC. A scenario is a VFR pilot taking off in VMC conditions, but encountering deteriorating visibility while en route. Continued VFR flight into IMC can lead to spatial disorientation of the pilot which is the cause of a significant number of general aviation crashes. VFR flight into IMC is distinct from "VFR-on-top", an IFR procedure in which the aircraft operates in VMC using a hybrid of VFR and IFR rules, and "VFR over the top", a VFR procedure in which the aircraft takes off and lands in VMC but flies above an intervening area of IMC. Also possible in many countries is "Special VFR" flight, where an aircraft is explicitly granted permission to operate VFR within the controlled airspace of an airport in conditions technically less than VMC; the pilot asserts they have the necessary visibility to fly despite the weather, must stay in contact with ATC, and cannot leave controlled airspace while still below VMC minimums.

During flight under IFR, there are no visibility requirements, so flying through clouds (or other conditions where there is zero visibility outside the aircraft) is legal and safe. However, there are still minimum weather conditions that must be present in order for the aircraft to take off or to land; these vary according to the kind of operation, the type of navigation aids available, the location and height of terrain and obstructions in the vicinity of the airport, equipment on the aircraft, and the qualifications of the crew. For example, Reno-Tahoe International Airport (KRNO) in a mountainous region has significantly different instrument approaches for aircraft landing on the same runway surface, but from opposite directions. Aircraft approaching from the north must make visual contact with the airport at a higher altitude than when approaching from the south because of rapidly rising terrain south of the airport. This higher altitude allows a flight crew to clear the obstacle if a landing is aborted. In general, each specific instrument approach specifies the minimum weather conditions to permit landing.

Although large airliners, and increasingly, smaller aircraft, carry their own terrain awareness and warning system (TAWS), these are primarily backup systems providing a last layer of defense if a sequence of errors or omissions causes a dangerous situation.

Navigation
Because IFR flights often take place without visual reference to the ground, a means of navigation other than looking outside the window is required. A number of navigational aids are available to pilots, including ground-based systems such as DME/VORs and NDBs as well as the satellite-based GPS/GNSS system. Air traffic control may assist in navigation by assigning pilots specific headings ("radar vectors"). The majority of IFR navigation is given by ground- and satellite-based systems, while radar vectors are usually reserved by ATC for sequencing aircraft for a busy approach or transitioning aircraft from takeoff to cruise, among other things.

Procedures
Specific procedures allow IFR aircraft to transition safely through every stage of flight. These procedures specify how an IFR pilot should respond, even in the event of a complete radio failure, and loss of communications with ATC, including the expected aircraft course and altitude.

Departures are described in an IFR clearance issued by ATC prior to takeoff. The departure clearance may contain an assigned heading, one or more waypoints, and an initial altitude to fly. The clearance can also specify a departure procedure (DP) or standard instrument departure (SID) that should be followed unless "NO DP" is specified in the notes section of the filed flight plan.

En route flight is described by IFR charts showing navigation aids, fixes, and standard routes called airways. Aircraft with appropriate navigational equipment such as GPS, are also often cleared for a direct-to routing, where only the destination, or a few navigational waypoints are used to describe the route that the flight will follow. ATC will assign altitudes in its initial clearance or amendments thereto, and navigational charts indicate minimum safe altitudes for airways.

The approach portion of an IFR flight may begin with a standard terminal arrival route (STAR), describing common routes to fly to arrive at an initial approach fix (IAF) from which an instrument approach commences. An instrument approach terminates either by the pilot acquiring sufficient visual reference to proceed to the runway, or with a missed approach because the required visual reference is not seen in time.

Pilot
To fly under IFR, a pilot must have an instrument rating and must be current (meet recency of experience requirements). In the United States, to file and fly under IFR, a pilot must be instrument-rated and, within the preceding six months, have flown six instrument approaches, as well as holding procedures and course interception and tracking with navaids. Flight under IFR beyond six months after meeting these requirements is not permitted; however, currency may be reestablished within the next six months by completing the requirements above. Beyond the twelfth month, examination ("instrument proficiency check") by an instructor is required.

Practicing instrument approaches can be done either in the instrument meteorological conditions or in visual meteorological conditions – in the latter case, a safety pilot is required so that the pilot practicing instrument approaches can wear a view-limiting device which restricts his field of view to the instrument panel. A safety pilot's primary duty is to observe and avoid other traffic.

In the UK, an IR (UK restricted) - formerly the "IMC rating" - which permits flight under IFR in airspace classes B to G in instrument meteorological conditions, a non-instrument-rated pilot can also elect to fly under IFR in visual meteorological conditions outside controlled airspace. Compared to the rest of the world, the UK's flight crew licensing regime is somewhat unusual in its licensing for meteorological conditions and airspace, rather than flight rules.

Aircraft
The aircraft must be equipped and type-certified for instrument flight, and the related navigational equipment must have been inspected or tested within a specific period of time prior to the instrument flight.

In the United States, instruments required for IFR flight in addition to those that are required for VFR flight are: heading indicator, sensitive altimeter adjustable for barometric pressure, clock with a sweep-second pointer or digital equivalent, attitude indicator, radios and suitable avionics for the route to be flown, alternator or generator, gyroscopic rate-of-turn indicator that is either a turn coordinator or the turn and bank indicator. From 1999 single-engine helicopters could not be FAA-certified for IFR. Recently, however, Bell and Leonardo have certified the single engine helicopters for instrument flight rules.

title: Instrument flight rules


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Ismail Khan

Mohammad Ismail Khan (Dari/Pashto: محمد اسماعیل خان) (born 1946) is an Afghan former politician who served as Minister of Energy and Water from 2005 to 2013 and before that served as the governor of Herat Province. Originally a captain in the Afghan Army, he is widely known as a former warlord who controlled a large mujahideen force, mainly his fellow Tajiks from western Afghanistan, during the Soviet–Afghan War.

His reputation gained him the nickname Lion of Herat. Ismail Khan was a key member of the now exiled political party Jamiat-e Islami and of the now defunct United National Front party. In 2021, Ismail Khan returned to arms to help defend Herat from the Taliban's offensive, which he and the Afghan Army lost. He was captured by the Taliban forces  and then reportedly fled to Iran on 16 August 2021.

Early years and rise to power
Khan was born in 1946 in the Shindand District of Herat Province in Afghanistan and his family is from the Chahar-Mahal neighbourhood of Shindand.

In early 1979 Ismail Khan was a captain in the Afghan National Army based in the western city of Herat. In early March of that year, there was a protest in front of the Communist governor's palace against the arrests and assassinations being carried out in the countryside by the Khalq government. The governor's troops opened fire on the demonstrators, who proceeded to storm the palace and hunt down Soviet advisers. The Herat garrison mutinied and joined the revolt in what is called the Herat uprising, with Ismail Khan and other officers distributing all available weapons to the insurgents. The government led by Nur Mohammed Taraki responded, pulverizing the city using Soviet supplied bombers and killing up to 24,000 citizens in less than a week. This event marked the opening salvo of the rebellion which led to the Soviet military intervention in Afghanistan in December 1979. Ismail Khan escaped to the countryside where he began to assemble a local rebel force.

During the ensuing war, he became the leader of the western command of Burhanuddin Rabbani's Jamiat-e-Islami, political party. With Ahmad Shah Massoud, he was one of the most respected mujahideen leaders. In 1992, three years after the Soviet withdrawal from Afghanistan, the mujahideen captured Herat and Ismail Khan became governor.

In 1995, he successfully defended his province against the Taliban, in cooperation with defense minister Ahmad Shah Massoud. Khan even tried to attack the Taliban stronghold of Kandahar, but was repulsed. Later in September, an ally of the Jamiat, Uzbek General Abdul Rashid Dostum changed sides, and attacked Herat. Ismail Khan was forced to flee to neighboring Iran with 8,000 men and the Taliban took over Herat Province.

Two years later, while organizing opposition to the Taliban in Faryab area, he was betrayed and captured by Abdul Majid Rouzi who had defected to the Taliban along with Abdul Malik Pahlawan, then one of Dostum's deputies. Then in March 1999 he escaped from Kandahar prison. During the U.S. intervention in Afghanistan, he fought against the Taliban within the United Islamic Front for the Salvation of Afghanistan (Northern Alliance) and thus regained his position as Governor of Herat after they were victorious in December 2001.

Karzai administration and return to Afghanistan
After returning to Herat, Ismail Khan quickly consolidated his control over the region. He took over control of the city from the local ulema and quickly established control over the trade route between Herat and Iran, a large source of revenue. As Emir of Herat, Ismail Khan exercised great autonomy, providing social welfare for Heratis, expanding his power into neighbouring provinces, and maintaining direct international contacts. Although hated by the educated in Herat and often accused of human rights abuses, Ismail Khan's regime provided security, paid government employees, and made investments in public services. However, during his tenure as governor, Ismail Khan was accused of ruling his province like a private fiefdom, leading to increasing tensions with the Afghan Transitional Administration. In particular, he refused to pass on to the government the revenues gained from custom taxes on goods from Iran and Turkmenistan.

On 13 August 2003, President Karzai removed Governor Ismail Khan from his command of the 4th Corps. This was announced as part of a programme removing the ability of officials to hold both civilian and military posts.

Ismail Khan was ultimately removed from power in March 2004 due to pressure by neighbouring warlords and the central Afghan government. Various sources have presented different versions of the story, and the exact dynamics cannot be known with certainty. What is known is that Ismail Khan found himself at odds with a few regional commanders who, although theoretically his subordinates, attempted to remove him from power. Ismail Khan claims that these efforts began with a botched assassination attempt. Afterwards, these commanders moved their forces near Herat. Ismail Khan, unpopular with the Herati military class, was slow to mobilise his forces, perhaps waiting for the threat to Herat to become existential as a means to motivate his forces. However, the conflict was stopped with the intervention of International Security Assistance Force forces and soldiers of the Afghan National Army, freezing the conflict in its tracks. Ismail Khan's forces even fought skirmishes with the Afghan National Army, in which his son, Mirwais Sadiq was killed. Because Ismail Khan was contained by the Afghan National Army, the warlords who opposed him were quickly able to occupy strategic locations unopposed. Ismail Khan was forced to give up his governorship and to go to Kabul, where he served in Hamid Karzai's cabinet as the Minister of Energy.

In 2005 Ismail Khan became the Minister of Water and Energy.

In late 2012, the Government of Afghanistan accused Ismail Khan of illegally distributing weapons to his supporters. About 40 members of the country's Parliament requested Ismail Khan to answer their queries. The government believes that Khan is attempting to create some kind of disruption in the country.

Assassination attempt
On September 27, 2009, Ismail Khan survived a suicide blast that killed 4 of his bodyguards in Herat, in western Afghanistan. He was driving to Herat Airport when a powerful explosion occurred close to his convoy of vehicles. Taliban spokesman Zabiullah Mujahid claimed responsibility and said Khan was the target.

Testimony requested by a Guantanamo captive
Guantanamo captive Abdul Razzaq Hekmati requested Ismail Khan's testimony, when he was called before a Combatant Status Review Tribunal. Ismail Khan, like Afghan Minister of Defense Rahim Wardak, was one of the high-profile Afghans that those conducting the Tribunals ruled were "not reasonably available" to give a statement on a captive's behalf because they could not be located.

Hekmati had played a key role in helping Ismail Khan escape from the Taliban in 1999. Hekmati stood accused of helping Taliban leaders escape from the custody of Hamid Karzai's government.

Carlotta Gall and Andy Worthington interviewed Ismail Khan for a new The New York Times article after Hekmati died of cancer in Guantanamo. According to the New York Times Ismail Khan said he personally buttonholed the American ambassador to tell him that Hekmati was innocent, and should be released. In contrast, Hekmati was told that the State Department had been unable to locate Khan.

2021 Taliban offensive and capture
In July 2021, Ismail Khan mobilized hundreds of his loyalists in Herat in support of the Afghan Armed Forces to defend the city from an offensive by the Taliban. Despite this, the city fell on 12 August 2021. After trying to escape by helicopter, Khan was captured by the Taliban. The Taliban interviewed him shortly after and claimed that he and his forces have joined them. After negotiating with the Taliban, he was allowed to return to his residence.

After leaving Taliban custody, as of August 2021 Khan is living in Mashhad, Iran. He said that a conspiracy was responsible for Herat being captured by the Taliban.

Controversy
Ismail Khan is a controversial figure. Reporters Without Borders has charged him with muzzling the press and ordering attacks on journalists. Also Human Rights Watch has accused him of human rights abuses.

Nevertheless, he remains a popular figure for some in Afghanistan. Unlike other mujahideen commanders, Khan has not been linked to large-scale massacres and atrocities such as those committed after the capture of Kabul in 1992. Following news of his dismissal, rioting broke out in the streets of Herat, and President Karzai had to ask him to make a personal appeal for calm.

title: Ismail Khan


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Indigo

Indigo is a term used for a number of hues in the region of blue. The word comes from the ancient dye of the same name. The term "indigo" can refer to the color of the dye, various colors of fabric dyed with indigo dye, a spectral color, one of the seven colors of the rainbow as described by Newton, or a region on the color wheel, and can include various shades of blue, ultramarine, and green-blue. Since the web era, the term has also been used for various purple and violet hues identified as "indigo", based on use of the term "indigo" in HTML web page specifications.

The word "indigo" comes from the Latin word indicum, meaning "Indian", as the naturally based dye was originally exported to Europe from India.

The Early Modern English word indigo referred to the dye, not to the color (hue) itself, and indigo is not traditionally part of the basic color-naming system.

The first known recorded use of indigo as a color name in English was in 1289.

Isaac Newton regarded indigo as a color in the visible spectrum, as well as one of the seven colors of the rainbow: the color between blue and violet; however, sources differ as to its actual position in the electromagnetic spectrum. Later scientists have concluded that what Newton called "blue" was what is now called cyan or blue-green; and what Newton called "indigo" was what is now called blue.

In the 1980s, programmers produced a somewhat arbitrary list of color names for the X Window computer operating system, resulting in the HTML and CSS specifications issued in the 1990s using the term "indigo" for a dark purple hue. This has resulted in violet and purple hues also being associated with the term "indigo" since that time.

Because of the Abney effect, pinpointing indigo to a specific hue value in the HSV color wheel is elusive, as a higher HSV saturation value shifts the hue towards blue. However, on the new CIECAM16 standard, the hues values around 290° may be thought of as indigo, depending on the observer.

Indigo as a dye

Indigo dye is a blue color, obtained from several different types of plants. The indigo plant (Indigofera tinctoria) often called "true indigo" probably produces the best results, although several others are close in color: Japanese indigo (Polygonum tinctoria), Natal indigo (Indigofera arrecta), Guatemalan indigo (Indigofera suffruticosa), Chinese indigo (Persicaria tinctoria), and woad Isatis tinctoria.

Indigofera tinctoria and related species were cultivated in East Asia, Egypt, India, Bangladesh and Peru in antiquity. The earliest direct evidence for the use of indigo dates to around 4000 BC and comes from Huaca Prieta, in contemporary Peru. Pliny the Elder mentions India as the source of the dye after which it was named. It was imported from there in small quantities via the Silk Road.

The Ancient Greek term for the dye was Ἰνδικὸν φάρμακον (indikon pharmakon, "Indian dye"), which, adopted to Latin as indicum (a second declension noun) or indico (oblique case) and via Portuguese, gave rise to the modern word indigo.

In early Europe the main source was from the woad plant Isatis tinctoria, also known as pastel. For a long time, woad was the main source of blue dye in Europe. Woad was replaced by "true indigo", as trade routes opened up. Plant sources have now been largely replaced by synthetic dyes.

Spanish explorers discovered an American species of indigo and began to cultivate the product in Guatemala. The English and French subsequently began to encourage indigo cultivation in their colonies in the West Indies.

In North America, indigo was introduced by Eliza Lucas into colonial South Carolina, where it became the colony's second-most important cash crop (after rice). Before the Revolutionary War, indigo accounted for more than one-third of the value of exports from the American colonies.

Isaac Newton's classification of indigo as a spectral color

Isaac Newton introduced indigo as one of the seven base colors of his work. In the mid-1660s, when Newton bought a pair of prisms at a fair near Cambridge, the East India Company had begun importing indigo dye into England, supplanting the homegrown woad as source of blue dye. In a pivotal experiment in the history of optics, the young Newton shone a narrow beam of sunlight through a prism to produce a rainbow-like band of colors on the wall. In describing this optical spectrum, Newton acknowledged that the spectrum had a continuum of colors, but named seven: "The originall or primary colours are Red, yellow, Green, Blew, & a violet purple; together with Orang, Indico, & an indefinite varietie of intermediate gradations." He linked the seven prismatic colors to the seven notes of a western major scale, as shown in his color wheel, with orange and indigo as the semitones. Having decided upon seven colors, he asked a friend to repeatedly divide up the spectrum that was projected from the prism onto the wall: "I desired a friend to draw with a pencil lines cross the image, or pillar of colours, where every one of the seven aforenamed colours was most full and brisk, and also where he judged the truest confines of them to be, whilst I held the paper so, that the said image might fall within a certain compass marked on it. And this I did, partly because my own eyes are not very critical in distinguishing colours, partly because another, to whom I had not communicated my thoughts about this matter, could have nothing but his eyes to determine his fancy in making those marks." Indigo is therefore counted as one of the traditional colors of the rainbow, the order of which is given by the mnemonics "Richard of York gave battle in vain" and Roy G. Biv. James Clerk Maxwell and Hermann von Helmholtz accepted indigo as an appropriate name for the color flanking violet in the spectrum.

Later scientists concluded that Newton named the colors differently from current usage. According to Gary Waldman, "A careful reading of Newton's work indicates that the color he called indigo, we would normally call blue; his blue is then what we would name blue-green or cyan." If this is true, Newton's seven spectral colors would have been: Red: Orange: Yellow: Green: Blue: Indigo: Violet:

The human eye does not readily differentiate hues in the wavelengths between what are now called blue and violet. If this is where Newton meant indigo to lie, most individuals would have difficulty distinguishing indigo from its neighbors. According to Isaac Asimov, "It is customary to list indigo as a color lying between blue and violet, but it has never seemed to me that indigo is worth the dignity of being considered a separate color. To my eyes, it seems merely deep blue."

1800s
In 1821, Abraham Werner published Werner's Nomenclature of Colours, where indigo, called indigo blue, is classified as a blue hue, and not listed among the violet hues. He writes that the color is composed of "Berlin blue, a little black, and a small portion of apple green," and indicating it is the color of blue copper ore, with Berlin blue being described as the color of a blue jay's wing, a hepatica flower, or a blue sapphire.

According to an article, Definition of the Color Indigo published in Nature magazine in the late 1800s, Newton's use of the term "indigo" referred to a spectral color between blue and violet. However, the article states that Wilhelm von Bezold, in his treatise on color, disagreed with Newton's use of the term, on the basis that the pigment indigo was a darker hue than the spectral color; and furthermore, Professor Ogden Rood points out that indigo pigment corresponds to the cyan-blue region of the spectrum, lying between blue and green, although darker in hue. Rood considers that artificial ultramarine pigment is closer to the point of the spectrum described as "indigo", and proposed renaming that spectral point as "ultramarine". The article goes on to state that comparison of the pigments, both dry and wet, with Maxwell's discs and with the spectrum, that indigo is almost identical to Prussian blue, stating that it "certainly does not lie on the violet side of 'blue.'" When scraped, a lump of indigo pigment appears more violet, and if powdered or dissolved, becomes greenish.

Modern spectral classification
Several modern sources place indigo in the electromagnetic spectrum between 420 and 450 nanometers, which lies on the short-wave side of color wheel (RGB) blue, towards (spectral) violet.

The correspondence of this definition with colors of actual indigo dyes, though, is disputed. Optical scientists Hardy and Perrin list indigo as between 445 and 464 nm wavelength, which occupies a spectrum segment from roughly the color wheel (RGB) blue extending to the long-wave side, towards azure.

Other modern color scientists, such as Bohren and Clothiaux (2006), and J.W.G. Hunt (1980), divide the spectrum between violet and blue at about 450 nm, with no hue specifically named indigo.

Origin of "Indigo" as a name for purple in web pages
Towards the end of the 20th century, purple colors also became referred to as "indigo". In the 1980s, computer programmers Jim Gettys, Paul Ravelling, John C. Thomas and Jim Fulton produced a list of colors for the X Window Operating System. The color identified as "indigo" was not the color indigo (as generally understood at the time), but was actually a dark purple hue; the programmers assigned it the hex code #4B0082. This collection of color names was somewhat arbitrary: Thomas used a box of 72 Crayola crayons as a standard, whereas Ravelling used color swabs from the now-defunct Sinclair Paints company, resulting in the color list for version X11 of the operating system containing fanciful color names such as "papaya whip", "blanched almond" and "peach puff". The database was also criticised for its many inconsistencies, such as "dark gray" being lighter than "gray", and for the color distribution being uneven, tending towards reds and greens at the expense of blues.

In the 1990s, this list which came with version X11 became the basis of the HTML and CSS color rendition used in websites and web design. This resulted in the name "Indigo" being associated with purple and violet hues in web page design and graphic design. Physics author John Spacey writes on the website Simplicable that the X11 programmers did not have any background in color theory, and that as these names are used by web designers and graphic designers, the name indigo has since that time been strongly associated with purple or violet. Spacey writes, "As such, a few programmers accidentally repurposed a color name that was known to civilisations for thousands of years."

Crayola crayon colors
The Crayola company released an indigo crayon in 1999, with the Crayola website using the hex code #4F49C6 to approximate the crayon color. The 2001 iron indigo crayon is portrayed using hex code #184FA1, the 2004 indigo crayon color uses #5D76CB , the 2019 iridescent indigo uses #3C32CD.

Distinction among tones of indigo
Like many other colors (orange, rose, and violet are the best-known), indigo gets its name from an object in the natural world—the plant named indigo once used for dyeing cloth (see also Indigo dye).

The color pigment indigo is equivalent to the web color indigo and approximates the color indigo that is usually reproduced in pigments and colored pencils.

The color of indigo dye is a different color from either spectrum indigo or pigment indigo. This is the actual color of the dye. A vat full of this dye is a darker color, approximating the web color midnight blue.

The color "electric indigo" is a bright and saturated color between the traditional indigo and violet. This is the brightest color indigo that can be approximated on a computer screen; it is a color located between the (primary) blue and the color violet of the RGB color wheel.

The web color blue violet or deep indigo is a tone of indigo brighter than pigment indigo, but not as bright as electric indigo.

Listed below are several indigo hues, some of which have included the word "indigo", with the adoption of HTML color names in the World Wide Web era.

Indigo dye color
Indigo dye is a greenish dark blue color, obtained from either the leaves of the tropical Indigo plant (Indigofera), or from woad (Isatis tinctoria), or the Chinese indigo (Persicaria tinctoria). Many societies make use of the Indigofera plant for producing different shades of blue. Cloth that is repeatedly boiled in an indigo dye bath-solution (boiled and left to dry, boiled and left to dry, etc.), the blue pigment becomes darker on the cloth. After dyeing, the cloth is hung in the open air to dry.

A Native American woman described the process used by the Cherokee Indians when extracting the dye: "We raised our indigo which we cut in the morning while the dew was still on it; then we put it in a tub and soaked it overnight, and the next day we foamed it up by beating it with a gourd. We let it stand overnight again, and the next day rubbed tallow on our hands to kill the foam. Afterwards, we poured the water off, and the sediment left in the bottom we would pour into a pitcher or crock to let it get dry, and then we would put it into a poke made of cloth (i.e. sack made of coarse cloth) and then when we wanted any of it to dye [there]with, we would take the dry indigo."

In Sa Pa, Vietnam, the tropical Indigo (Indigo tinctoria) leaves are harvested and, while still fresh, placed inside a tub of room-temperature to lukewarm water where they are left to sit for 3 to 4 days and allowed to ferment, until the water turns green. Afterwards, crushed limestone (pickling lime) is added to the water, at which time the water with the leaves are vigorously agitated for 15 to 20 minutes, until the water turns blue. The blue pigment settles as sediment at the bottom of the tub. The sediment is scooped out and stored. When dyeing cloth, the pigment is then boiled in a vat of water; the cloth (usually made from yarns of hemp) is inserted into the vat for absorbing the dye. After hanging out to dry, the boiling process is repeated as often as needed to produce a darker color.

Indigo (color wheel)
In a RGB color space, "Indigo(color wheel)" is composed of 25.1% red, 0% green and 100% blue. Whereas in a CMYK color space, it is composed of 74.9% cyan, 100% magenta, 0% yellow and 0% black. It has a hue angle of 255.1 degrees, a saturation of 100% and a lightness of 50%. Indigo(color wheel) could be obtained by blending violet with blue.

Electric indigo
"Electric indigo" is brighter than the pigment indigo reproduced above. When plotted on the CIE chromaticity diagram, this color is at 435 nanometers, in the middle of the portion of the spectrum traditionally considered indigo, i.e., between 450 and 420 nanometers. This color is only an approximation of spectral indigo, since actual spectral colors are outside the gamut of the sRGB color system.

Deep indigo (web color blue-violet)
At right is displayed the web color "blue-violet", a color intermediate in brightness between electric indigo and pigment indigo. It is also known as "deep indigo".

Web color indigo
The color box on the right displays the web color indigo, the color indigo as it would be reproduced by artists' paints as opposed to the brighter indigo above (electric indigo) that is possible to reproduce on a computer screen. Its hue is closer to violet than to indigo dye for which the color is named. Pigment indigo can be obtained by mixing 55% pigment cyan with about 45% pigment magenta.

Compare the subtractive colors to the additive colors in the two primary color charts in the article on primary colors to see the distinction between electric colors as reproducible from light on a computer screen (additive colors) and the pigment colors reproducible with pigments (subtractive colors); the additive colors are significantly brighter because they are produced from light instead of pigment.

Web color indigo represents the way the color indigo was always reproduced in pigments, paints, or colored pencils in the 1950s. By the 1970s, because of the advent of psychedelic art, artists became accustomed to brighter pigments. Pigments called "bright indigo" or "bright blue-violet" (the pigment equivalent of the electric indigo reproduced in the section above) became available in artists' pigments and colored pencils.

Tropical indigo
'Tropical Indigo' is the color that is called añil in the Guía de coloraciones (Guide to colorations) by Rosa Gallego and Juan Carlos Sanz, a color dictionary published in 2005 that is widely popular in the Hispanophone realm.

Birds

 * Male indigobirds are a very dark, metallic blue.
 * The indigo bunting, native to North America, is mostly bright cerulean blue with an indigo head.
 * The related blue grosbeak is, ironically, more indigo than the indigo bunting.

Fungi

 * Lactarius indigo is one of the very few species of mushrooms colored in tones of blue.

Snakes

 * The eastern indigo snake, Drymarchon couperi, of the southeastern United States, is a dark blue/black.

Business

 * IndiGo is an Indian budget airline that uses an indigo logo and operates only Airbus A320s.
 * Indigo Books and Music uses an indigo logo and has sometimes referred to the color as "blue" in advertising.
 * The GameCube was initially released in 2 color variants, including one bearing the title of 'Indigo', with the main console and controllers in that color.

Computer graphics

 * Electric indigo is sometimes used as a glow color for computer graphics lighting, possibly because it seems to change color from indigo to lavender when blended with white.

Dyes

 * Indigo dye was used to dye denim, giving the original 'blue jeans' their distinctive colour.
 * The original Postal Worker uniform contained indigo dye, partly due to the dye not running when wet.
 * Guatemala, as of 1778, was considered one of the world's foremost providers of indigo.
 * In Mexico, indigo is known as añil. After silver, and cochineal to produce red, añil was the most important product exported by historical Mexico.
 * The use of añil is survived in the Philippines, particularly in the Visayas and Mindanao. The powder dye is mixed with vinegar to be applied to the cheek of a person suffering from mumps.

Food

 * Scientists discovered in 2008 that when a banana becomes ripe, it glows bright indigo under a black light. Some insects, as well as birds, see into the ultraviolet, because they are tetrachromats and can use this information to tell when a banana is ready to eat. The glow is the result of a chemical created as the green chlorophyll in the peel breaks down.

Literature
Marina Warner's novel Indigo (1992) is a retelling of Shakespeare's The Tempest and features the production of indigo dye by Sycorax.

Military
The French Army adopted dark blue indigo at the time of the French Revolution, as a replacement for the white uniforms previously worn by the Royal infantry regiments. In 1806, Napoleon decided to restore the white coats because of shortages of indigo dye imposed by the British continental blockade. However, the greater practicability of the blue color led to its retention, and indigo remained the dominant color of French military coats until 1914.

Popular culture
In the Better Call Saul episode "Hero", Howard Hamlin mentions that his law firm Hamlin Hamlin & McGill trademarked a colour called "Hamlindigo" whilst confronting Jimmy McGill over trademark infringement in a billboard advertisement he produced for his own legal services.

Spirituality
The spiritualist applications use electric indigo, because the color is positioned between blue and violet on the spectrum.
 * The color electric indigo is used in New Age philosophy to symbolically represent the sixth chakra (called Ajna), which is said to include the third eye. This chakra is believed to be related to intuition and gnosis (spiritual knowledge).
 * Alice A. Bailey used indigo as the "second ray", representing "Love-Wisdom", in her Seven Rays system classifying people into seven metaphysical psychological types.
 * Psychics often associate indigo paranormal auras with an interest in religion or with intense spirituality and intuition. Indigo children are said to have predominantly indigo auras. People with indigo auras are said to favor occupations such as computer analyst, animal caretaker, and counselor.
 * In Wicca, it represents emotion, fluidity, insight, and expressiveness. It is used to spiritually heal.

title: Indigo