∀ a0. a0 ∈ s → a0 = a ⊦ # s = 0, s = ∅, s = ∅ ++ a, a ∈ ∅
Used simplifier rules: eq: ⊦ a ∈ s → s ++ a = s;%In-empty: ⊦ ¬ a ∈ ∅; Used formulas: a ∈ ∅