`{Funext} (n : nat) {A B : Type} (C : B -> Type) (f : A -> B) : ExtendableAlong n.+2 f C <~> IsEquiv (fun (g : forall b, C b) => g oD f). Proof. etransitivity. - apply equiv_extendable_pathsplit. - apply equiv_pathsplit_isequiv. Defined.
Require Import HoTT.Basics HoTT.Types. Require Import Equiv.PathSplit Homotopy.IdentitySystems. Require Import Cubical.DPath Cubical.DPathSquare. Require Import Colimits.Coeq Colimits.MappingCylinder.