apply System.not_reducible_iff.mpr
α : Type u_1
inst✝¹ : DecidableEq α
p : Formula α
inst✝ : Inhabited α
⊢ ¬𝐒𝟒 ≤ₛ 𝐆𝐋
α : Type u_1
inst✝¹ : DecidableEq α
p : Formula α
inst✝ : Inhabited α
⊢ ∃ f, 𝐒𝟒 ⊢! f ∧ 𝐆𝐋 ⊬! f