⊦ st1 = st2 ↔ (∀ a. (a ∈ st1 ↔ a ∈ st2) ∧ st1[a] = st2[a])
⊦ ∀ a0. (a0 ∈ (st -- b)[a, d] ↔ a0 ∈ st[a, d] -- b) ∧ (st -- b)[a, d][a0] = (st[a, d] -- b)[a0], a = b
Used terms: st[a, d] -- b, (st -- b)[a, d]