proposition: Lemma oddg_iter_face i d : oddg (iter i gface d) = iter i ccw (oddg d).
proof: Proof. by elim: i => //= i IHi; rewrite oddg_face IHi. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq path) mathcomp(div choice order ssralg ssrnum ssrint intdiv) fourcolor(hypermap)