st = ∅ ⊦ ¬(∃ a, d, st0. st = st0[a, d] ∧ ¬ a ∈ st0)
¬(∃ a, d, st0. st = st0[a, d] ∧ ¬ a ∈ st0) ⊦ st = ∅