proposition: Lemma invUg A B : (A :|: B)^-1 = A^-1 :|: B^-1.
proof: Proof. exact: preimsetU. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq choice) mathcomp(fintype div path tuple bigop prime finset)