{X} {a : X} (u : idpath a = idpath a) {v w : idpath a = idpath a} (p : v = 1) (q : 1 = w) : (ehlnat u p [-] ehlnat u q) @ whiskerL _ (whiskerR_pp _ p q)^ = (whiskerR (whiskerL_pp _ p q)^ _) @ ehlnat u (p @ q). Proof. revert v p. snrapply (equiv_path_ind (equiv_path_inverse _)). destruct q. apply rlucancel, lrucancel_sVs_1. Defined.
From HoTT Require Import Basics Types.