⊦ S ⊆ S0 ↔ (∀ x. S(x) → S0(x))
S0(x0), f(S0)(x), ∀ x. S0(x) → S(x), f(λ x0. ∃ n. (n = 0 ⊃ S0;S)(x0))(x) ⊦ S(x0), f(S)(x)
Used terms: S, S0