Structure

Implication details

Claim: If a category is cartesian closed and has a strict terminal object, then it is thin.

Proof: If a morphism X→YX \to Y exists, we get a morphism 1→[X,Y]1 \to [X,Y], which forces [X,Y][X,Y] to be a terminal object by assumption. But then any two morphisms 1⇉[X,Y]1 \rightrightarrows [X,Y] are equal, so that any two morphisms X⇉YX \rightrightarrows Y are equal.

This implication has a dual.

Show 26 categories using this implication