出典:Wikipedia
出典:『Wikipedia』 (2011/05/13 07:06 UTC 版)
In mathematics, a binary relation, R, is well-founded (or wellfounded) on a class X if and only if every non-empty subset of X has a minimal element with respect to R; that is, for every non-empty subset S of X, there is an element m of S such that for every element s of S, the pair (s,m) is not in R: