fact: Definition isequiv_commsq' {A B C D} (f : A -> B) (g : C -> D) (h : A -> C) (k : B -> D) (p : g o h == k o f) `{IsEquiv _ _ g} `{IsEquiv _ _ h} `{IsEquiv _ _ k} : IsEquiv f.
imports: Basics.Overture Basics.PathGroupoids Basics.Contractible Basics.Tactics