proposition: Lemma zvalid_init : zvalid p0l p0r.
proof: Proof. by rewrite /zvalid catrev_part_eq Dp0l rev_rev_part. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(fintype path fingraph) fourcolor(hypermap geometry part quiz quiztree)