proposition: Lemma orbit_eqP G x y : reflect (orbit to G x = orbit to G y) (x \in orbit to G y).
proof: Proof. exact/orbit_in_eqP/subsetT. Qed.
imports: mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat div seq) mathcomp(fintype bigop finset fingroup morphism perm) mathcomp(automorphism quotient)