⊦ (a ∈ st → a ∈ ∅ ⊕ st) ∧ (a ∈ ∅ ⊕ st → (∅ ⊕ st)[a] = st[a])
Used simplifier rules: oplus-l-in: ⊦ a ∈ st0 ⊕ st1 ↔ a ∈ st0 ∨ a ∈ st1;%In-empty: ⊦ ¬ a ∈ ∅; from specification store