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In topology, a preclosure operator, or Čech closure operator is a map between subsets of a set, similar to a topological closure operator, except that it is not required to be idempotent. That is, a preclosure operator obeys only three of the four Kuratowski closure axioms. == Definition == A preclosure operator on a set is a map : where is the power set of . The preclosure operator has to satisfy the following properties: # (Preservation of nullary unions); # (Extensivity); # (Preservation of binary unions). The last axiom implies the following: : 4. implies . 抄文引用元・出典: フリー百科事典『 ウィキペディア(Wikipedia)』 ■ウィキペディアで「preclosure operator」の詳細全文を読む スポンサード リンク
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