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出典:Wiktionary
出典:Wikipedia
出典:『Wikipedia』 (2010/12/17 13:20 UTC 版)
In mathematics, a directed set (or a directed preorder or a filtered set) is a nonempty set A together with a reflexive and transitive binary relation ≤ (that is, a preorder), with the additional property that every pair of elements has an upper bound: In other words, for any a and b in A there must exist a c in A with a ≤ c and b ≤ c.