proposition: Lemma expgM x n m : x ^+ (n * m) = x ^+ n ^+ m.
proof: Proof. elim: m => [|m IHm]; first by rewrite muln0 expg0. by rewrite mulnS expgD IHm expgS. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq choice) mathcomp(fintype div path tuple bigop prime finset)