proposition: Lemma coset_reprK : cancel (fun xbar => repr xbar) coset.
proof: Proof. by move=> xbar; apply: coset_mem (mem_repr_coset xbar). Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq div) mathcomp(choice fintype prime finset fingroup morphism) mathcomp(automorphism)