⊦ S ⊆ S0 ↔ (∀ x. S(x) → S0(x))
S0(x0), f(λ x0. ¬ S(x0))(x), ∀ x. S0(x) → S(x) ⊦ S(x0), f(λ x0. ¬ S0(x0))(x)
Used terms: S, S0