a ∈ st ⊦ ∃ d, st0. (∀ a0. (a0 ∈ st ↔ a0 ∈ st0[a, d]) ∧ st[a0] = st0[a, d][a0]) ∧ ¬ a ∈ st0
Used simplifier rules: Extension: ⊦ st1 = st2 ↔ (∀ a. (a ∈ st1 ↔ a ∈ st2) ∧ st1[a] = st2[a]);