∀ {ι : Type u_1} [inst : DecidableEq ι] (A : ι → Type u_2) [inst_1 : (i : ι) → AddCommGroup (A i)]
  [inst_2 : AddMonoid ι] (g h : A 0), (DirectSum.of A 0) (g - h) = (DirectSum.of A 0) g - (DirectSum.of A 0) h