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