∀ {R : Type u_1} {ι : Type u_2} {A : Type u_3} {B : Type u_4} [inst : CommSemiring ι] [inst_1 : DecidableEq ι]
  [inst_2 : CommRing R] [inst_3 : Ring A] [inst_4 : Ring B] [inst_5 : Algebra R A] [inst_6 : Algebra R B]
  (𝒜 : ι → Submodule R A) (ℬ : ι → Submodule R B) [inst_7 : GradedAlgebra 𝒜] [inst_8 : GradedAlgebra ℬ]
  [inst_9 : Module ι (Additive ℤˣ)] (a b c : GradedTensorProduct R 𝒜 ℬ), a * b * c = a * (b * c)