⊦ s1 = s2 ↔ (∀ a. a ∈ s1 ↔ a ∈ s2)
∀ a. a ∈ dom st ∩ s ↔ a ∈ ∅, a ∈ s ⊦ s = ∅, # s = 0, (a ∈ st \ s ↔ a ∈ st) ∧ (∅)[a] = st[a]
Used terms: ∅, dom st ∩ s