∀ {C : Type u_1} [inst : CategoryTheory.Category.{v_1, u_1} C],
  autoParam (∀ (X Y : C), Subsingleton (X ⟶ Y)) CategoryTheory.IsDiscrete.subsingleton._autoParam →
    (∀ {X Y : C} (f : X ⟶ Y), X = Y) → CategoryTheory.IsDiscrete C