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🔗 Mathematics

In geometry, the problem of dividing a circle into areas by means of an inscribed polygon with n sides in such a way as to maximise the number of areas created by the edges and diagonals, sometimes called Moser's circle problem, has a solution by an inductive method. The greatest possible number of regions, r_G = ( ⁿ
₄ ) + ( ⁿ
₂ ) + 1, giving the sequence 1, 2, 4, 8, 16, 31, 57, 99, 163, 256, ... (OEIS: A000127). Though the first five terms match the geometric progression 2^{n − 1}, it diverges at n = 6, showing the risk of generalising from only a few observations.

🔗 Computer science

Algorithm X is an algorithm for solving the exact cover problem. It is a straightforward recursive, nondeterministic, depth-first, backtracking algorithm used by Donald Knuth to demonstrate an efficient implementation called DLX, which uses the dancing links technique.

🔗 Mathematics 🔗 Statistics

In mathematics, the theory of optimal stopping or early stopping is concerned with the problem of choosing a time to take a particular action, in order to maximise an expected reward or minimise an expected cost. Optimal stopping problems can be found in areas of statistics, economics, and mathematical finance (related to the pricing of American options). A key example of an optimal stopping problem is the secretary problem. Optimal stopping problems can often be written in the form of a Bellman equation, and are therefore often solved using dynamic programming.

🔗 Novels 🔗 Slovenia

Alamut is a novel by Vladimir Bartol, first published in 1938 in Slovenian, dealing with the story of Hassan-i Sabbah and the Hashshashin, and named after their Alamut fortress. The maxim of the novel is "Nothing is an absolute reality; all is permitted". This book was one of the inspirations for the video game series Assassin's Creed.

Bartol first started to conceive the novel in the early 1930s, when he lived in Paris. In the French capital, he met with the Slovene literary critic Josip Vidmar, who introduced him to the story of Hassan-i Sabbah. A further stimulation for the novel came from the assassination of Alexander I of Yugoslavia perpetrated by Croatian and Bulgarian radical nationalists, on the alleged commission of the Italian fascist government. When it was originally published, the novel was sarcastically dedicated to Benito Mussolini.

🔗 Computing

Constraint logic programming is a form of constraint programming, in which logic programming is extended to include concepts from constraint satisfaction. A constraint logic program is a logic program that contains constraints in the body of clauses. An example of a clause including a constraint is A(X,Y) :- X+Y>0, B(X), C(Y). In this clause, X+Y>0 is a constraint; A(X,Y), B(X), and C(Y) are literals as in regular logic programming. This clause states one condition under which the statement A(X,Y) holds: X+Y is greater than zero and both B(X) and C(Y) are true.

As in regular logic programming, programs are queried about the provability of a goal, which may contain constraints in addition to literals. A proof for a goal is composed of clauses whose bodies are satisfiable constraints and literals that can in turn be proved using other clauses. Execution is performed by an interpreter, which starts from the goal and recursively scans the clauses trying to prove the goal. Constraints encountered during this scan are placed in a set called constraint store. If this set is found out to be unsatisfiable, the interpreter backtracks, trying to use other clauses for proving the goal. In practice, satisfiability of the constraint store may be checked using an incomplete algorithm, which does not always detect inconsistency.

🔗 Software 🔗 Software/Computing

In the context of Unix-like systems, the term rc stands for the phrase "run commands". It is used for any file that contains startup information for a command. It is believed to have originated sometime in 1965 at a runcom facility from the MIT Compatible Time-Sharing System (CTSS).

From Brian Kernighan and Dennis Ritchie:

There was a facility that would execute a bunch of commands stored in a file; it was called runcom for "run commands", and the file began to be called "a runcom". rc in Unix is a fossil from that usage.

Tom Van Vleck, a Multics engineer, has also reminisced about the extension rc: "The idea of having the command processing shell be an ordinary slave program came from the Multics design, and a predecessor program on CTSS by Louis Pouzin called RUNCOM, the source of the '.rc' suffix on some Unix configuration files."

This is also the origin of the name of the Plan 9 from Bell Labs shell by Tom Duff, the rc shell. It is called "rc" because the main job of a shell is to "run commands".

While not historically precise, rc may also be expanded as "run control", because an rc file controls how a program runs. For instance, the editor Vim looks for and reads the contents of the .vimrc file to determine its initial configuration. In The Art of Unix Programming, Eric S. Raymond consistently refers to rc files as "run-control" files.

🔗 Companies 🔗 Lists

This list of the oldest companies in the world includes brands and companies, excluding associations and educational, government, or religious organizations. To be listed, a brand or company name must remain operating, either in whole or in part, since inception. Note however that such claims are often open to question and should be researched further before citing them.

🔗 United States/U.S. Government 🔗 United States 🔗 Appalachia 🔗 National Archives 🔗 Tennessee 🔗 Energy 🔗 Alabama

The Tennessee Valley Authority (TVA) is a federally owned electric utility corporation in the United States. TVA's service area covers all of Tennessee, portions of Alabama, Mississippi, and Kentucky, and small areas of Georgia, North Carolina, and Virginia. While owned by the federal government, TVA receives no taxpayer funding and operates similarly to a private for-profit company. It is headquartered in Knoxville, Tennessee, and is the sixth-largest power supplier and largest public utility in the country.

The TVA was created by Congress in 1933 as part of President Franklin D. Roosevelt's New Deal. Its initial purpose was to provide navigation, flood control, electricity generation, fertilizer manufacturing, regional planning, and economic development to the Tennessee Valley, a region that had suffered from lack of infrastructure and even more extensive poverty during the Great Depression than other regions of the nation. TVA was envisioned both as a power supplier and a regional economic development agency that would work to help modernize the region's economy and society. It later evolved primarily into an electric utility. It was the first large regional planning agency of the U.S. federal government, and remains the largest.

Under the leadership of David E. Lilienthal, the TVA also became the global model for the United States' later efforts to help modernize agrarian societies in the developing world. The TVA historically has been documented as a success in its efforts to modernize the Tennessee Valley and helping to recruit new employment opportunities to the region. Historians have criticized its use of eminent domain and the displacement of over 125,000 Tennessee Valley residents to build the agency's infrastructure projects.

🔗 Biology 🔗 Physics 🔗 Economics 🔗 Philosophy 🔗 Systems 🔗 Philosophy/Philosophy of science 🔗 Philosophy/Epistemology

In philosophy, systems theory, science, and art, emergence occurs when an entity is observed to have properties its parts do not have on their own. These properties or behaviors emerge only when the parts interact in a wider whole. For example, smooth forward motion emerges when a bicycle and its rider interoperate, but neither part can produce the behavior on their own.

Emergence plays a central role in theories of integrative levels and of complex systems. For instance, the phenomenon of life as studied in biology is an emergent property of chemistry, and psychological phenomena emerge from the neurobiological phenomena of living things.

In philosophy, theories that emphasize emergent properties have been called emergentism. Almost all accounts of emergentism include a form of epistemic or ontological irreducibility to the lower levels.

🔗 Philosophy 🔗 Philosophy/Logic 🔗 Business 🔗 Politics 🔗 Psychology

In social psychology, fundamental attribution error (FAE), also known as correspondence bias or attribution effect, is the tendency for people to under-emphasize situational explanations for an individual's observed behavior while over-emphasizing dispositional and personality-based explanations for their behavior. This effect has been described as "the tendency to believe that what people do reflects who they are".