proposition: Lemma card_porbit_neq0 s x : #|porbit s x| != 0.
proof: Proof. by rewrite -lt0n card_gt0; apply/set0Pn; exists x; exact: porbit_id. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq path) mathcomp(choice fintype tuple finfun bigop finset binomial) mathcomp(fingroup morphism)