proposition: Lemma cface_node_ecpH : cface (node ecpH) (icpH (node x0)).
proof: Proof. by rewrite cface1 /= if_neg /=; do 2!rewrite nodeK (negPf x0gt1) /=. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(fintype path fingraph) fourcolor(hypermap geometry color)