proposition: Lemma comps_cons G H s : comps G (H :: s) -> comps H s.
proof: Proof. by case/andP => /= ls /andP[_]; rewrite /comps ls. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq path) mathcomp(choice fintype bigop finset fingroup morphism) mathcomp(automorphism quotient action gseries)