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