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