Structure

Implication details

Claim: If a category has kernel pairs and is retract-trivial, then it is left cancellative.

Proof: Let f:X→Yf : X \to Y be a morphism with kernel pair E⇉XE \rightrightarrows X. The diagonal X→EX \to E is a split monomorphism. By assumption on the category, it is an isomorphism. Therefore, X→idXXidX↓↓fX→fY\begin{CD} X @>{\id_X}>> X \\ @V{\id_X}VV @VV{f}V \\ X @>>{f}> Y \end{CD} is a pullback, so ff is a monomorphism.

This implication has a dual.

Show 15 categories using this implication