{A B C : Type} (P : C -> Type) (f : A -> B) (g : B -> C) : ooExtendableAlong g P -> ooExtendableAlong f (fun b => P (g b)) -> ooExtendableAlong (g o f) P := fun extg extf n => extendable_compose n P f g (extg n) (extf n).
Require Import HoTT.Basics HoTT.Types. Require Import Equiv.PathSplit Homotopy.IdentitySystems. Require Import Cubical.DPath Cubical.DPathSquare. Require Import Colimits.Coeq Colimits.MappingCylinder.