Talk:Kuratowski closure axioms
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How do you get axiom 4 (empty set is fixed point) from the single statement you have (pres. of finitary unions)? I don't see it. Unless you didn't mean that it was equivalent, that's what it sounds like. Revolver
It would be preservation of a nullary union. Not a big deal.
Charles Matthews 19:18, 1 Dec 2003 (UTC)
I changed this back to the plural article name, for basically the same reasons that the article is called Orthogonal polynomials, not "orthogonal polynomial", i.e. it doesn't make sense to talk about a "kuratowski closure axiom" simply by itself, it is the SET of all 4 axioms together that constitute the object we're talking about, just one or two of the axioms by themselves is not the same thing. Revolver 19:03, 2 Feb 2004 (UTC)
was first restricted to T1 not T2 (Hausdorff).
Moore requires 3) monotone this gives
<math> c(A) \cup c(B) \subseteq c(A \cup B)\! <math>;
Rewrote article
I rewrote and extended the article to make clear how other basic topological notions (like continuous function) can be defined using only the closure operator. MathMartin 17:35, 12 Mar 2005 (UTC)