| ordered≤(a ' + x1), x ⊒ a ' + x1, ∀ x0. x0 ⊒ x1 → ordered≤(x0) ⊦ ordered≤(x) |
⊦ x ≠ [] ∧ x.tail ≠ [] → (ordered≤(x) ↔ ¬ x.tail.head < x.head ∧ ordered≤(x.tail))
ordered≤(a ' + x1), x ⊒ a ' + x1, ∀ x0. x0 ⊒ x1 → ordered≤(x0) ⊦ ordered≤(x), a ' + x1 ≠ [] ∧ (a ' + x1).tail ≠ []
ordered≤((a ' + x1).tail), x ⊒ a ' + x1, ∀ x0. x0 ⊒ x1 → ordered≤(x0) ⊦ a ' + x1 = [], (a ' + x1).tail = [], (a ' + x1).tail.head < (a ' + x1).head, ordered≤(x)
Used terms: a ' + x1