| ⊦ s ++ a = ∅ ++ b ↔ a = b ∧ s = ∅, a ∈ s |
∀ a0. a0 = a ∨ a0 ∈ s ↔ a0 = b ⊦ a ∈ s, a = b ∧ ¬ a0 ∈ s
Used simplifier rules: Extension: ⊦ s1 = s2 ↔ (∀ a. a ∈ s1 ↔ a ∈ s2);%In-insert: ⊦ a ∈ s ++ b ↔ a = b ∨ a ∈ s;%in-04: ⊦ a ∈ ∅ ++ b ↔ a = b;%In-empty: ⊦ ¬ a ∈ ∅;