Separation of disjoint compact subsets
ID: separation-of-disjoint-compact-subsets
Two disjoint compact subsets of a Hausdorff space have disjoint open neighbourhoods. For every , separation of a point and a compact set gives disjoint open sets and . Choose finitely many covering , then take their union for and the matching finite intersection of the for . The compactness of both subsets is used, once in the point-versus-compact set result and once in the outer finite selection. The ambient Hausdorff space need not be compact or a normal space.
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