Talk:Door space

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ultrafilter

I found out about door spaces five minutes ago. Is it correct to say that a door space topology on X is an ultrafilter on X? If so, this should be pointed out. Tkuvho (talk) 15:59, 6 February 2012 (UTC)

A topology is never an ultrafilter, as the empty set is open. Note that the definition allows for a given set and its complement to be both open. Having said that, I have serious doubts about the notability of this concept.—Emil J. 18:55, 9 January 2015 (UTC)
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