proposition: Lemma slice_isBinProduct_to_isPullback {A B Z P : C} {f : A --> Z} {g : B --> Z} {l : P --> A} {r : P --> B} {e : l · f = r · g} : isBinProduct (C / Z) (A ,, f) (B ,, g) (P ,, l · f) (l ,, idpath _) (r ,, e) → isPullback e.
proof: Proof. intros PisProd Y j k Yeq. use unique_exists. + exact (pr1 (pr1 (pr1 (PisProd (Y ,, j · f) (j ,, idpath _) (k ,, Yeq))))). + abstract (exact (maponpaths pr1 (pr1 (pr2 (pr1 (PisProd (Y ,, j · f) (j ,, idpath _) (k ,, Yeq))))) ,, maponpaths pr1 (pr2 (pr2 (pr1 (PisProd (Y ,, j · f) (j ,, idpath _) (k ,, Yeq))))))). + abstract (intros x; apply isofhleveldirprod; apply C). + intros t teqs. use (maponpaths pr1 (maponpaths pr1 (pr2 (PisProd (Y ,, j · f) (j ,, idpath _) (k ,, Yeq)) ((t ,, (maponpaths (λ x, x · f) (!(pr1 teqs)) @ !(assoc _ _ _) @ maponpaths (λ x, t · x) (idpath _))) ,, _)))). abstract (split; apply eq_mor_slicecat; [exact (pr1 teqs) | exact (pr2 teqs)]). Defined.
imports: UniMath.MoreFoundations.Tactics UniMath.Foundations.Sets UniMath.CategoryTheory.Core.Categories UniMath.CategoryTheory.Core.Functors UniMath.CategoryTheory.slicecat UniMath.CategoryTheory.Equivalences.Core UniMath.CategoryTheory.Limits.BinProducts UniMath.CategoryTheory.Limits.Pullbacks