⊦ st1 = st2 ↔ (∀ a. (a ∈ st1 ↔ a ∈ st2) ∧ st1[a] = st2[a])
⊦ ∀ a0. (a0 ∈ st[a, d] \ s ↔ a0 ∈ (st \ s)[a, d]) ∧ (st[a, d] \ s)[a0] = (st \ s)[a, d][a0], a ∈ s
Used terms: (st \ s)[a, d], st[a, d] \ s