For a commutative square of functors that is a pullback in Cat, the mate of its identity 2-cell under adjunction is an isomorphism. In Set: pullback Σ-∃ commutes with substitution - the semantic content of 'descent of quantifiers'. Core…
For a commutative square of functors that is a pullback in Cat, the mate of its identity 2-cell under adjunction is an isomorphism. In Set: pullback Σ-∃ commutes with substitution - the semantic content of 'descent of quantifiers'. Core…