Description: There are no definable free ultrafilters in ZFC. However, there are free ultrafilters in some choice-denying constructions. Here we show that given an amorphous set (a.k.a. a Ia-finite I-infinite set) X , the set of infinite subsets of X is a free ultrafilter on X . (Contributed by Mario Carneiro, 20-May-2015)
Ref | Expression | ||
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Hypothesis | fin1aufil.1 | |
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Assertion | fin1aufil | |