proposition: Lemma bridgeless_ecpU : bridgeless ecpU.
proof: Proof. have X'eX: ~ cface ecpU (edge ecpU) by rewrite cface_ecpU. apply/existsP=> [] [[||x]] //; first by rewrite cfaceC. by rewrite cface_icpU bridgeless_cface. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(fintype path fingraph) fourcolor(hypermap geometry color)