| |
| | Dedekind cut - Freepedia (Site not responding. Last check: 2007-10-08) |
 | | In mathematics, a Dedekind cut in a totally ordered set S is a partition of it, (A, B), such that A is closed downwards (meaning that for any element x in S, if a is in A and x ≤ a, then x is in A as well) and B is closed upwards. |
 | | For example it is shown that the typical Dedekind cut in the real numbers is either a pair with A the interval (-∞,a), in which case B must be [a,+∞); or a pair with A the interval (-∞,a], in which case B must be (a,+∞). |
 | | The Dedekind cut is named after Richard Dedekind, who invented this construction in order to represent the real numbers as Dedekind cuts of the rational numbers. |
| en.freepedia.org /Dedekind_completion.html (506 words) |
|