a ∈ st ⊦ (∀ a0. (a0 ∈ st ↔ a0 ∈ (st -- a)[a, st[a]]) ∧ st[a0] = (st -- a)[a, st[a]][a0]) ∧ ¬ a ∈ st -- a
Used terms: st[a], st -- a