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are not simple for values <= .

There are four Hopf fibrations of hyperspheres:

They are defined as locally trivial fibrations that map for values of (aside from the trivial fibration mapping between two points and a circle).

In Knuth's up-arrow notation, , and so forth, for any number of up arrows.

There are four dimensions in the theory of Minkowski space, three of space and the one being time.

List of basic calculations

In culture

*Four is the sacred number of the Zia, an indigenous tribe located in the U.S. state of New Mexico.
*Superstition about the number four is most common in East Asian nations, where it is a homonym for "death" in many languages.

In technology

*In internet slang, "4" can replace the word "for" (as "four" and "for" are pronounced similarly). For example, messaging "4 u" instead of "for you" when talking to someone.
*In Leetspeak, "4" may be used to replace the letter "A".

Notes

References

*Wells, D. The Penguin Dictionary of Curious and Interesting Numbers London: Penguin Group. (1987): 55-58

External links

*
*, by Penelope Merritt at samuel-beckett.net
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