proposition: Lemma cardSg G H : H \subset G -> #|H| %| #|G|.
proof: Proof. by move/Lagrange <-; rewrite dvdn_mulr. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq choice) mathcomp(fintype div path tuple bigop prime finset)