proposition: Lemma fmodJ x y : y \in 'N(A) -> fmod (x ^ y) = fmod x ^@ y.
proof: Proof. move=> Ny; apply: val_inj; rewrite fmvalJ ?fmodKcond ?memJ_norm //. by case: ifP => // _; rewrite conj1g. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq path) mathcomp(div choice fintype bigop ssralg finset fingroup) mathcomp(morphism perm finalg action gproduct commutator) mathcomp(cyclic)