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