∀ {R : Type u_1} {A : Type u_2} {B : Type u_3} [inst : CommSemiring R] [inst_1 : NonUnitalNonAssocSemiring A]
  [inst_2 : NonUnitalNonAssocSemiring B] [inst_3 : Module R A] [inst_4 : Module R B] [inst_5 : SMulCommClass R A A]
  [inst_6 : SMulCommClass R B B] [inst_7 : IsScalarTower R A A] [inst_8 : IsScalarTower R B B] [inst_9 : StarRing R]
  [inst_10 : StarRing A] [inst_11 : StarRing B] [inst_12 : StarModule R A] [inst_13 : StarModule R B]
  (x y : TensorProduct R A B), star (x * y) = star y * star x