{A : Type} {g : A -> A} (p : forall x, x = g x) {x y : A} (q : x = y) {w : A} (r : w = x) : (r @ p x) @ ap g q = (r @ q) @ p y. Proof. destruct q; simpl. induction (p x). reflexivity. Defined.
Require Import Basics.Overture Basics.Tactics.