theorem LO.Modal.Hilbert.K4_weakerThan_KD4 {α : Type u_1} : LO.Modal.Hilbert.K4 α ≤ₛ LO.Modal.Hilbert.KD4 α

theorem LO.Modal.Hilbert.K4_strictlyWeakerThan_KD4 : LO.Modal.Hilbert.K4 ℕ <ₛ LO.Modal.Hilbert.KD4 ℕ