proposition: Lemma expg_cardG G a : a \in G -> a ^+ #|G| = 1.
proof: Proof. by move=> Ga; apply/eqP; rewrite -order_dvdn order_dvdG. 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)