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K-219 was a Project 667A Navaga-class ballistic missile submarine (NATO reporting name Yankee I) of the Soviet Navy. It carried 16 R-27U liquid-fuel missiles powered by UDMH with nitrogen tetroxide (NTO), and equipped with either 32 or 48 nuclear warheads.K-219 was involved in what has become one of the most controversial submarine incidents during the Cold War on Friday 3 October 1986. The 15-year-old vessel, which was on an otherwise routine Cold War nuclear deterrence patrol in the North Atlantic 1,090 kilometres (680 mi) northeast of Bermuda, suffered an explosion and fire in a missile tube. While underway submerged the seal in a missile hatch cover failed, allowing high-pressure seawater to enter the missile tube and owing to the pressure differential rupture the missile fuel tanks, allowing missile's liquid fuel to mix and ultimately combust. Though there was no official announcement, the Soviet Union claimed the leak was caused by a collision with the submarine USS Augusta. Although Augusta was operating within the area, both the United States Navy and the commander of K-219, Captain Second Rank Igor Britanov, deny that a collision took place.

The incident was novelized in the book Hostile Waters, which reconstructed the incident from descriptions by the survivors, ships' logs, the official investigations, and participants both ashore and afloat from the Soviet and the American sides.

In 2011, Randall Munroe in his comic xkcd coined the term "citogenesis" to describe the creation of "reliable" sources through circular reporting. This is a list of some well-documented cases where Wikipedia has been the source.

The Symmetry454 calendar (Sym454) is a proposal for calendar reform created by Irv Bromberg of the University of Toronto, Canada. It is a perennial solar calendar that conserves the traditional month pattern and 7-day week, has symmetrical equal quarters in 82% of the years in its 293-year cycle, and starts every month on Monday.

The "rural purge" of American television networks (in particular CBS) was a series of cancellations in the early 1970s of still-popular rural-themed shows with demographically skewed audiences, the majority of which occurred at the end of the 1970–71 television season. In addition to rural-themed shows such as Mayberry R.F.D., The Beverly Hillbillies, and Green Acres, the cancellations ended several highly rated variety shows that had been on CBS since the beginning of television broadcasting. CBS saw a dramatic change in direction with the shift, moving away from shows with rural themes and toward more appeal to urban and suburban audiences.

.su was assigned as the country code top-level domain (ccTLD) for the Soviet Union (USSR) on 19 September 1990. Even though the Soviet Union itself was dissolved a mere 15 months later, the .su top-level domain remains in use today. It is administered by the Russian Institute for Public Networks (RIPN, or RosNIIROS in Russian transcription).

Quantum tic-tac-toe is a "quantum generalization" of tic-tac-toe in which the players' moves are "superpositions" of plays in the classical game. The game was invented by Allan Goff of Novatia Labs, who describes it as "a way of introducing quantum physics without mathematics", and offering "a conceptual foundation for understanding the meaning of quantum mechanics".

Von Neumann's elephant is a problem in recreational mathematics, consisting of constructing a planar curve in the shape of an elephant from only four fixed parameters. It originated from a discussion between physicists John von Neumann and Enrico Fermi.

Säkkijärven polkka ("the Säkkijärvi polka"), also called the "Karelian-Finnish Polka," is a well-known folk tune from Finland, very popular with Finnish accordionists. It was especially popularized by Viljo "Vili" Vesterinen (1907–1961). The tune was first recorded in Säkkijärvi (now Kondratyevo in the Leningrad Oblast, Russia), and the lyrics sometimes sung with the tune state that while Säkkijärvi itself might have been lost (ceded to the Soviet Union in 1940), the Finns at least still had the polka.

Alternative 3 is a television programme, broadcast once only in the United Kingdom in 1977, and later broadcast in Australia, Canada, and New Zealand, as a fictional hoax, an heir to Orson Welles' radio production of The War of the Worlds. Purporting to be an investigation into the UK's contemporary "brain drain", Alternative 3 uncovered a plan to make the Moon and Mars habitable in the event of climate change and a terminal environmental catastrophe on Earth.

The programme was originally meant to be broadcast on April Fools' Day, 1977. While its broadcast was delayed until 20 June, the credits explicitly date the film to 1 April. Alternative 3 ended with credits for the actors involved in the production and featured interviews with a fictitious American astronaut.

A negative base (or negative radix) may be used to construct a non-standard positional numeral system. Like other place-value systems, each position holds multiples of the appropriate power of the system's base; but that base is negative—that is to say, the base b is equal to −r for some natural number r (r ≥ 2).

Negative-base systems can accommodate all the same numbers as standard place-value systems, but both positive and negative numbers are represented without the use of a minus sign (or, in computer representation, a sign bit); this advantage is countered by an increased complexity of arithmetic operations. The need to store the information normally contained by a negative sign often results in a negative-base number being one digit longer than its positive-base equivalent.

The common names for negative-base positional numeral systems are formed by prefixing nega- to the name of the corresponding positive-base system; for example, negadecimal (base −10) corresponds to decimal (base 10), negabinary (base −2) to binary (base 2), negaternary (base −3) to ternary (base 3), and negaquaternary (base −4) to quaternary (base 4).