proposition: Lemma cface_ecpK : cface ecpK (icpK (face (edge x0))).
proof: Proof. rewrite /ecpK ecpR1_eq ecpR'_eq /= nodeK; case: ifP => // /eqP. by rewrite (@cface1 (ecpN _)) nodeK /= => {3}->; rewrite nodeK. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(fintype path fingraph) fourcolor(hypermap geometry color)