{A B} {f : A -> B} {g : B -> A} {x1 x2 : A} (p : x1 = x2) (q : x1 = g (f x1)) r : (p^ @ q) @ ap g (ap f p) = r <~> DPath (fun x : A => x = g (f x)) p q r. Proof. apply equiv_concat_l, transport_paths_lFFr. Defined.
Require Import Basics. Require Import Types.Paths Types.Sigma Types.Forall.