proposition: Lemma eq_n_comp_r {e} a a' : a =i a' -> n_comp e a = n_comp e a'.
proof: Proof. by move=> eq_a; apply: eq_card => x; rewrite inE /= eq_a. Qed.
imports: mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat) mathcomp(seq path fintype)