proposition: Lemma cface_ecpU : cface ecpU =1 xpred1 (ecpU : ecpU).
proof: Proof. by move=> u; rewrite /= -mem_seq1; apply: fconnect_cycle. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(fintype path fingraph) fourcolor(hypermap geometry color)