Description: For any point of an open set of the usual topology on ( RR X. RR ) there is an open square which contains that point and is entirely in the open set. This is square is actually a ball by the ( l ^ +oo ) norm X . (Contributed by Thierry Arnoux, 21-Sep-2017)
Ref | Expression | ||
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Hypotheses | tpr2rico.0 | |
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tpr2rico.1 | |
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tpr2rico.2 | |
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Assertion | tpr2rico | |