Description: Lemma for poimir , two ways of expressing the property that a face is not on the back face of the cube. (Contributed by Brendan Leahy, 21-Aug-2020)
Ref | Expression | ||
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Hypotheses | poimir.0 | |
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poimirlem23.1 | |
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poimirlem23.2 | |
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poimirlem23.3 | |
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Assertion | poimirlem23 | |