⊦ s1 = s2 ↔ (∀ a. a ∈ s1 ↔ a ∈ s2)
Used simplifier rules: Keys: ⊦ a ∈ st.keys ↔ a ∈ st;% ⊦ ¬ a ∈ ∅; (s)% ⊦ ¬ a ∈ ∅; (s) Used terms: ∅, ∅.keys