Solved cryptogram

Give a strip of paper a half twist and tape the ends, and the loop you get has only one side.

Mathematics Facts, sourced to Wolfram MathWorld.

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What it means

Run a pencil along the surface without lifting it and you return to where you started having covered what looks like both faces. It has one edge too. Cutting it down the middle does not give you two loops; it gives one longer loop with a couple of twists in it. The shape is a standard first example of a surface that cannot be consistently assigned an inside and an outside.

The claim comes from Wolfram MathWorld.

Nearby in the collection

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