ultrafilter

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earthquake. Heavily damaged school in the town of Yingxiu after a major earthquake struck China's Sichuan Province on May 12, 2008.

The 6 Deadliest Earthquakes Since 1950

The Cheshire Cat is a fictional cat from Lewis Carroll's Alice's Adventures in Wonderland. (Alice in Wonderland)

11 Banned Books Through Time

Artist interpretation of a Space meteoroid impact. Meteor impact. Asteroid, End of the world, danger, destruction, dinosaur extinct, Judgement Day, Planet Earth, Doomsday Predictions, comet

10 Failed Doomsday Predictions

Orange basketball on black background and with low key lighting. Homepage 2010, arts and entertainment, history and society

The 10 Greatest Basketball Players of All Time

John F. Kennedy as a boy with his family

What Did We Call America’s Elite Before the “1 Percent”?

Thanksgiving Celebration Traditional Dinner Setting Food Concept

Why Is Thanksgiving in the U.S. Celebrated on a Thursday?

New York NY/ USA- November 23, 2018 Hordes of shoppers throng the Macy's Herald Square flagship store in New York looking for bargains on the day after Thanksgiving, Black Friday.

Why Is It Called Black Friday?

ultrafilter

logic

Learn about this topic in these articles:

model theory

In metalogic: Ultrafilters, ultraproducts, and ultrapowers
) An ultrafilter on a nonempty set I is defined as a set D of subsets of I such that
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