proposition: Lemma bifunctor_comp_left {A B C : category} (F : A ⊠ B ⟶ C) {a a' a'' : A} {b : B} (f : a --> a') (g : a' --> a'') : #F (f · g #, identity b) = #F (f #, identity _) · #F (g #, identity _).
proof: Proof. rewrite <- (functor_comp F). change ((?x #, ?y) · (?z #, ?w)) with (x · z #, y · w). rewrite id_left. reflexivity. Qed.
imports: UniMath.Foundations.PartA UniMath.Foundations.Propositions UniMath.CategoryTheory.Core.Categories UniMath.CategoryTheory.Core.Functors UniMath.CategoryTheory.Core.NaturalTransformations UniMath.CategoryTheory.Monoidal.Categories UniMath.CategoryTheory.PrecategoryBinProduct UniMath.CategoryTheory.Core.Isos