proposition: Lemma porbitsV s : porbits s^-1 = porbits s.
proof: Proof. rewrite /porbits; apply/setP => y. by apply/imsetP/imsetP => -[x _ ->{y}]; exists x; rewrite // porbitV. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq path) mathcomp(choice fintype tuple finfun bigop finset binomial) mathcomp(fingroup morphism)