proposition: Lemma zvalid_initl : zvalid p0ll p0lr.
proof: Proof. move: Ep0r; rewrite -size_rev_part -Dp0l -nFx0 -orderSpred /zvalid -zvalid_init. by case p0l. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(fintype path fingraph) fourcolor(hypermap geometry part quiz quiztree)