∀ {R : Type u_3} {A : Type u_4} {B : Type u_1} {M : Type u_2} [inst : CommSemiring R] [inst_1 : AddCommMonoid M]
  [inst_2 : Module R M] [inst_3 : Semiring A] [inst_4 : Semiring B] [inst_5 : Module A M] [inst_6 : Module B M]
  [inst_7 : Algebra R A] [inst_8 : Algebra R B] [inst_9 : IsScalarTower R A M] [inst_10 : IsScalarTower R B M]
  (r t : A),
  (r + t) • (Algebra.lsmul R R M).toLinearMap =
    r • (Algebra.lsmul R R M).toLinearMap + t • (Algebra.lsmul R R M).toLinearMap