∀ {ι : Type u_1} {R : Type u_2} {A : Type u_3} [inst : DecidableEq ι] [inst_1 : AddMonoid ι] [inst_2 : CommSemiring R]
  [inst_3 : Semiring A] [inst_4 : Algebra R A] (𝒜 : ι → Submodule R A) [inst_5 : GradedAlgebra 𝒜] (a : A),
  (DirectSum.decomposeAlgEquiv 𝒜) a = (DirectSum.decompose 𝒜) a