∀ {R : Type u} [inst : NonAssocSemiring R] [inst_1 : PartialOrder R] [CanonicallyOrderedAdd R] [inst_3 : Sub R]
  [OrderedSub R] [Std.Total fun x1 x2 => x1 ≤ x2] [AddLeftReflectLE R] (a b : R), a * (b - 1) = a * b - a