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