∀ a. a ∈ x0 → (∃ y, z. x0 = y + a ' + z ∧ ¬ a ∈ z), a ∈ a0 + x0 ⊦ ∃ y, z. a0 + x0 = y + a ' + z ∧ ¬ a ∈ z
Used simplifier rules: in-empty: ⊦ ¬ a ∈ [];%list freely generated by [], +;;