Description: Lemma for heibor . Using countable choice ax-cc , we have fixed in advance a collection of finite 2 ^ -u n nets ( Fn ) for X (note that an r -net is a set of points in X whose r -balls cover X ). The set G is the subset of these points whose corresponding balls have no finite subcover (i.e. in the set K ). If the theorem was false, then X would be in K , and so some ball at each level would also be in K . But we can say more than this; given a ball ( y B n ) on level n , since level n + 1 covers the space and thus also ( y B n ) , using heiborlem1 there is a ball on the next level whose intersection with ( y B n ) also has no finite subcover. Now since the set G is a countable union of finite sets, it is countable (which needs ax-cc via iunctb ), and so we can apply ax-cc to G directly to get a function from G to itself, which points from each ball in K to a ball on the next level in K , and such that the intersection between these balls is also in K . (Contributed by Jeff Madsen, 18-Jan-2014)
Ref | Expression | ||
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Hypotheses | heibor.1 | |
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heibor.3 | |
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heibor.4 | |
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heibor.5 | |
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heibor.6 | |
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heibor.7 | |
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heibor.8 | |
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Assertion | heiborlem3 | |