The boundary of a solid hypercube?
\partial(I\times I\times I\times I) |
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\partial((I\times I)\times(I\times I)) |
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= |
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\partial(\square\times\square) |
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= |
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(\partial\,\square\times \square)\cup (\square\times
\partial\,\square) |
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= |
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(\box\times\square)\cup(\square\times\box) |
Two congruent pieces, but what are they?
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