fact: Definition isequiv_extendable `{Funext} (n : nat) {A B : Type} {C : B -> Type} {f : A -> B} : ExtendableAlong n.+2 f C -> IsEquiv (fun g => g oD f) := isequiv_pathsplit n o (equiv_extendable_pathsplit n.+2 C f).
imports: HoTT.Basics HoTT.Types Equiv.PathSplit PathAny Cubical.DPath Cubical.DPathSquare Colimits.Coeq Colimits.MappingCylinder