proposition: Lemma pathp_rev x y p : pathp x y p -> pathp y x (srev x p).
proof: Proof. rewrite /pathp. elim/last_ind: p => /= [|p z _]; first by rewrite eq_sym. rewrite !srev_rcons !last_rcons eqxx andbT path_srev last_rcons srev_rcons. by move/andP => [A /eqP <-]. Qed.
imports: Coq(Setoid CMorphisms) mathcomp(all_ssreflect) GraphTheory(edone preliminaries bij digraph)