proposition: Lemma zproper_stepR zp : zproper (zstepR zp) -> zproper zp.
proof: Proof. by case: zp => -[]. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(fintype path fingraph) fourcolor(hypermap geometry part quiz quiztree)