proposition: Lemma eq_invg_sym x y : (x^-1 == y) = (x == y^-1).
proof: Proof. by apply: (inv_eq invgK). Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq choice) mathcomp(fintype div path tuple bigop prime finset)