proposition: Lemma mem_porbit s i x : (s ^+ i) x \in porbit s x.
proof: Proof. by rewrite [@porbit]unlock (imset_f (aperm x)) ?mem_cycle. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq path) mathcomp(choice fintype tuple finfun bigop finset binomial) mathcomp(fingroup morphism)