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