CatDat

Implication Details

Claim: If a category has binary powers and is core-thin, then it is thin.

Proof: Let XX be any object. The swap τ:X×XX×X\tau : X \times X \to X \times X is an automorphism, hence equal to the identity. It follows that the projections p1,p2:X×XXp_1,p_2 : X \times X \rightrightarrows X are the same. And this means that every two morphisms YXY \rightrightarrows X are the same.

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