proposition: Lemma cface_icpN : {mono icpN : x y / cface x y}.
proof: Proof. by move=> x y; have [_ ->] := adjnF_ecpN. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(fintype path fingraph) fourcolor(hypermap geometry color)