proposition: Lemma closed_Gr : fclosed edge (codom hr).
proof: Proof. apply: (intro_closed cedgeC) => x _ /eqP <- xrP. by rewrite -(f_iinv xrP) -hrE codom_f. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(fintype path fingraph) fourcolor(hypermap geometry jordan color coloring)