| true, ∀ x1, x2. # x1 + # x2 < # x + # x0 → true → x1 + x2 = [] ∨ max(x1 + x2) = max(x2 + x1) ⊦ x + x0 = [] ∨ max(x + x0) = max(x0 + x) |
∀ x1, x2. # x1 + # x2 < # x + # x0 → true → x1 + x2 = [] ∨ max(x1 + x2) = max(x2 + x1) ⊦ x + x0 = [], max(x + x0) = max(x0 + x)