proposition: Lemma baseN_ecpU : fun_base icpU node node (pred1 (Icp (node x0))).
proof: Proof. by move=> x y; rewrite /= -if_neg => ->. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(fintype path fingraph) fourcolor(hypermap geometry color)