true, ∀ x1, x2. #(x1 + x2) < #(x + x0) → true → x1 + x2 = [] ∨ min(x1 + x2) = min(x2 + x1) ⊦ x + x0 = [] ∨ min(x + x0) = min(x0 + x)
Used simplifier rules: <; (wellfounded) Used terms: #(x + x0)