∀ m, a. # x0 = m + 1 ∧ a ∈ x0 → #(x0 -1l a) = m ∨ x0 = [], #(a0 + x0) = m + 1, a ∈ a0 + x0 ⊦ #((a0 + x0) -1l a) = m, a0 + x0 = []
Used simplifier rules: list freely generated by [], +;;