proposition: Lemma bridgeless_ecpY : bridgeless ecpY.
proof: Proof. have /idP X'eX := cface_ecpY (edge ecpY). have /idP fX'efX := cface_ecpY (edge (face ecpY)); rewrite cface1 in fX'efX. apply/existsP=> [] [] [||[||x]] //; try by rewrite cfaceC. by rewrite cface_icpY bridgeless_cface. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(fintype path fingraph) fourcolor(hypermap geometry color)