∀ {ι : Type u_1} {R : Type u_3} {A : ι → Type u_4} [inst : CommSemiring R]
  [inst_1 : (i : ι) → NonUnitalNonAssocSemiring (A i)] [inst_2 : (i : ι) → Module R (A i)]
  [inst_3 : ∀ (i : ι), SMulCommClass R (A i) (A i)] [inst_4 : ∀ (i : ι), IsScalarTower R (A i) (A i)],
  PiTensorProduct.mul = PiTensorProduct.piTensorHomMap₂ ((PiTensorProduct.tprod R) fun x => LinearMap.mul R (A x))