| x0.last < a, max(x0) = x0.last, ordered≤(a ' + x0) ⊦ a = x0.last, x0 = [] |
⊦ ordered≤(y) ↔ # y ≤ 1 ∨ ¬ y.rest.first < y.first ∧ ordered≤(y.rest)
x0.last < a, max(x0) = x0.last, #(a ' + x0) ≤ 1 ∨ ¬ (a ' + x0).rest.first < (a ' + x0).first ∧ ordered≤((a ' + x0).rest) ⊦ a = x0.last, x0 = []
Used terms: a ' + x0