| (a0 + x0) -1l a = [], ∀ a. x0 -1l a = [] → x0 = [] ∨ x0 = a ' ⊦ a0 + x0 = a ', a0 + x0 = [] |
(a0 ' + x0) -1l a = [], ∀ a. x0 -1l a = [] → x0 = [] ∨ x0 = a ' ⊦ a0 ' + x0 = a '
Used simplifier rules: a: ⊦ (x + y) + z = x + y + z; from specification list% ⊦ a ' + x ≠ []; (s)% ⊦ a + x = a ' + x; (s)