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In decision theory, the sure-thing principle states that a decision maker who would take a certain action if he knew that event E has occurred, and also if he knew that the negation of E has occurred, should also take that same action if he knows nothing about E.

The principle was coined by L.J. Savage:

A businessman contemplates buying a certain piece of property. He considers the outcome of the next presidential election relevant. So, to clarify the matter to himself, he asks whether he would buy if he knew that the Democratic candidate were going to win, and decides that he would. Similarly, he considers whether he would buy if he knew that the Republican candidate were going to win, and again finds that he would. Seeing that he would buy in either event, he decides that he should buy, even though he does not know which event obtains, or will obtain, as we would ordinarily say. It is all too seldom that a decision can be arrived at on the basis of this principle, but except possibly for the assumption of simple ordering, I know of no other extralogical principle governing decisions that finds such ready acceptance.

He formulated the principle as a dominance principle, but it can also be framed probabilistically. Richard Jeffrey and later Judea Pearl showed that Savage's principle is only valid when the probability of the event considered (e.g., the winner of the election) is unaffected by the action (buying the property). Under such conditions, the sure-thing principle is a theorem in the do-calculus (see Bayes networks). Blyth constructed a counterexample to the sure-thing principle using sequential sampling in the context of Simpson's paradox, but this example violates the required action-independence provision.

The principle is closely related to independence of irrelevant alternatives, and equivalent under the axiom of truth (everything the agent knows is true). It is similarly targeted by the Ellsberg and Allais paradoxes, in which actual people's choices seem to violate this principle.

The X-Seed 4000 is a visionary skyscraper for what would be, if it was built, the tallest building in the world. The idea was initially created and developed by Peter Neville. Its proposed 4-kilometre (2.5 mi) height, 6-kilometre-wide (3.7 mi) sea-base, and 800-floor capacity could accommodate 500,000 to 1,000,000 inhabitants. This structure would be composed of over 3,000,000 tons of pure steel.

It was designed for Tokyo, Japan by the Taisei Corporation in 1995 as a futuristic environment combining ultra-modern living and interaction with nature. Methods of transportation within the X-seed would most likely include MagLev trains.

The X-Seed 4000 "is never meant to be built," says Georges Binder, managing director of Buildings & Data, a firm which compiles data banks on buildings worldwide. "The purpose of the plan was to earn some recognition for the firm, and it worked."

Unlike conventional skyscrapers, to remain habitable the (X-Seed 4000) would be forced to actively protect its occupants from considerable internal air pressure and external air pressure gradations and weather fluctuations that its massive elevation would cause. Its design calls for the use of solar power to maintain internal environmental conditions. As the proposed site for the structure is located in the Pacific Ring of Fire, the most active volcano range in the world, the X-Seed 4000 would be subject to earthquakes and tsunamis.

A sea-based location and a Mount Fuji shape are some of this building's other major design features—the real Mount Fuji is land-based and is 3,776 metres (12,388 ft) high so is 224 metres (735 ft) shorter than the X-Seed 4000.

The X-Seed 4000 is projected to be twice the height of the Shimizu Mega-City Pyramid at 2,004 metres (6,575 ft). The Shimizu Mega-City Pyramid (proposed in 2007, also planned for Tokyo, Japan) faces most of the same problems as the X-Seed. Other projects that may be in the top five man made structures are the Ultima Tower 3,218 metres (10,558 ft) in San Francisco, Dubai City Tower 2,400 metres (7,900 ft) and the Bionic Tower 1,228 metres (4,029 ft) in either Hong Kong or Shanghai.

A rolleron is a type of aileron used for rockets, placed at the trailing end of each fin, and used for passive stabilization against rotation. Inherent to the rolleron is a metal wheel with notches along the circumference. On one side, the notches protrude into the airflow. During flight, this will spin the wheels up to a substantial speed. The wheels then act as gyroscopes. Any tendency of the rocket to rotate around its major axis will be counteracted by the rollerons: the gyroscopic precession acts to move the rolleron in the opposite direction to the rotation.

Rollerons were first used in the AIM-9 Sidewinder missile.

Edward Elgar composed his Variations on an Original Theme, Op. 36, popularly known as the Enigma Variations, between October 1898 and February 1899. It is an orchestral work comprising fourteen variations on an original theme.

Elgar dedicated the work "to my friends pictured within", each variation being a musical sketch of one of his circle of close acquaintances (see musical cryptogram). Those portrayed include Elgar's wife Alice, his friend and publisher Augustus J. Jaeger and Elgar himself. In a programme note for a performance in 1911 Elgar wrote:

This work, commenced in a spirit of humour & continued in deep seriousness, contains sketches of the composer's friends. It may be understood that these personages comment or reflect on the original theme & each one attempts a solution of the Enigma, for so the theme is called. The sketches are not 'portraits' but each variation contains a distinct idea founded on some particular personality or perhaps on some incident known only to two people. This is the basis of the composition, but the work may be listened to as a 'piece of music' apart from any extraneous consideration.

In naming his theme "Enigma", Elgar posed a challenge which has generated much speculation but has never been conclusively answered. The Enigma is widely believed to involve a hidden melody.

After its 1899 London premiere the Variations achieved immediate popularity and established Elgar's international reputation.

Xennials or xennials (also known as the Oregon Trail Generation and Generation Catalano) are the micro-generation of people on the cusp of the Generation X and Millennial demographic cohorts. Researchers and popular media use birth years from the late 1970s to the early 1980s. Xennials are described as having had an analog childhood and a digital young adulthood.

In 2020, xennial was included in the Oxford Dictionary of English.

OSCAR I (aka OSCAR 1) is the first amateur radio satellite launched by Project OSCAR into low Earth orbit. OSCAR I was launched December 12, 1961, by a Thor-DM21 Agena B launcher from Vandenberg Air Force Base, Lompoc, California. The satellite, a rectangular box (30 x 25 x 12 cm) weighing 10 kg., was launched as a secondary payload (ballast) for Corona 9029, also known as Discoverer 36, the eighth and final launch of a KH-3 satellite.

The satellite had a battery-powered 140 mW transmitter operating in the 2-meter band (144.983 MHz), employed a monopole transmitting antenna 60 cm long extended from the center of the convex surface, but had no attitude control system. Like Sputnik 1, Oscar 1 carried only a simple beacon. For three weeks it transmitted its Morse Code message "HI". To this day, many organizations identify their Morse-transmitting satellites with "HI", which also indicates laughter in amateur telegraphy.

OSCAR I lasted 22 days ceasing operation on January 3, 1962, and re-entered January 31, 1962.

The uniqueness of the OSCAR-1 spacecraft was not only that it was built by amateurs, only about four years after the launch of Sputnik-1, but that it was the world's first piggyback satellite and the world's first private non-government spacecraft.

Immediately following the launch of OSCAR-1, United States vice president, Lyndon B. Johnson, honored it with a congratulatory telegram to the group sponsoring this momentous event in the history of Amateur Radio. It read: “For me this project is symbolic of the type of freedom for which this country stands — freedom of enterprise and freedom of participation on the part of individuals throughout the world.”

The original backup of OSCAR-1 has been restored and is fully operational, running off AC power. As of 2011 it is on display at ARRL HQ in Newington, Connecticut and continues to broadcast "HI" in Morse Code at 145 MHz.

Spondylus is a genus of bivalve molluscs, the only genus in the family Spondylidae. They are known in English as spiny oysters or thorny oysters (though they are not, in fact, true oysters).

The bus service from London, England to Calcutta, India (now Kolkata) was considered to be the longest bus route in the world. The bus service, which started in 1957, was routed to India via Belgium, Yugoslavia and North Western India. This route is also known as the Hippie Route. According to reports, it took about 50 days for the bus to reach Calcutta from London. The voyage was over 10,000 miles (16,000 km) one way and 20,300 miles (32,700 km) for the round trip. It was in service until 1976. The cost of the trip one-way was £85 in 1957 and £145 in 1973. This amount included food, travel and accommodation.

Thokcha (Tibetan: ཐོག་ལྕགས, Wylie: thog lcags; also alternatively Tibetan: གནམ་ལྕགས, Wylie: gnam lcags) are tektites and meteorites which serve as amulets. Typically high in iron content, these are traditionally believed to contain a magical, protective power comparable to Tibetan dzi beads. Most thokcha are made of a copper alloy.

The use of meteoric iron has been common throughout the history of ferrous metallurgy. Historically, thokcha were prized for the metallurgical fabrication of weapons, musical instruments, and sacred tools, such as the phurba. Thokcha are an auspicious addition in the metallurgical fabrication of sacred objects cast from panchaloha.

Writer Robert Beer regards meteoric iron as "the supreme substance for forging the physical representation of the vajra or other iron weapons." It was believed that these amulets had been tempered by the celestial gods before falling to Earth. Beer describes the metal falling from space as a metaphor for "the indivisibility of form and emptiness." Many meteorite fragments can be found in Tibet due to its high altitude and open landscape.

Tang ping (Chinese: 躺平; pinyin: tǎng píng; lit. 'lying flat') is a lifestyle choice and social protest movement in China by some young people who reject societal pressures on hard work or even overwork (such as the 996 working hour system, which is generally regarded as a rat race with ever diminishing returns), and instead choose to "lie down flat and get over the beatings" via a low-desire, more indifferent attitude towards life. Novelist Liao Zenghu described "lying flat" as a resistance movement, and The New York Times called it part of a nascent Chinese counterculture. It has also been compared to the Great Resignation that began in America (and the western world) around the same time.

Unlike the hikikomori in Japan (who are socially withdrawn), these young Chinese people who subscribe to "lying flat" are not socially isolated, but merely choose to lower their professional and economic ambitions and simplify their goals, still being fiscally productive for their own essential needs, and prioritize psychological health over economic materialism.