proposition: Lemma no_adj_adj x y1 y2 : ~~ adj x y1 -> adj x y2 -> cface y1 y2 = false.
proof: Proof. by move=> xA'y1 xAy2; apply: contraNF xA'y1 => /adjFr->. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(fintype path fingraph) fourcolor(hypermap jordan)