Description: The "tube lemma". If X is compact and there is an open set U containing the line X X. { A } , then there is a "tube" X X. u for some neighborhood u of A which is entirely contained within U . (Contributed by Mario Carneiro, 21-Mar-2015)
Ref | Expression | ||
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Hypotheses | txtube.x | |
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txtube.y | |
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txtube.r | |
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txtube.s | |
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txtube.w | |
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txtube.u | |
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txtube.a | |
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Assertion | txtube | |