proposition: Lemma generator_order a b : generator <[a]> b -> #[a] = #[b].
proof: Proof. by rewrite /order => /(<[a]> =P _)->. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq choice div) mathcomp(fintype bigop prime finset fingroup morphism) mathcomp(perm automorphism quotient gproduct ssralg) mathcomp(finalg zmodp poly)