∀ {ι : Type u_2} {M : ι → Type u_1} [inst : (i : ι) → AddCommMonoid (M i)] [inst_1 : DecidableEq ι] (i : ι) (x y : M i),
  (↑(DFinsupp.singleAddHom M i)).toFun (x + y) =
    (↑(DFinsupp.singleAddHom M i)).toFun x + (↑(DFinsupp.singleAddHom M i)).toFun y