proposition: Lemma order_dvdn a n : #[a] %| n = (a ^+ n == 1).
proof: Proof. by rewrite (eq_expg_mod_order a n 0) mod0n. 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)