⊦ st1 = st2 ↔ (∀ a. (a ∈ st1 ↔ a ∈ st2) ∧ st1[a] = st2[a])
∀ a. ¬ a ∈ st0 ∪ st1 ∧ st1[a] = (∅)[a] ⊦ ¬ a ∈ st0 ∧ (∀ a. (a ∈ st1 ↔ a ∈ ∅) ∧ st1[a] = (∅)[a])
Used terms: ∅, st1