x + y + z ⊑ y ⊦ x = [] ∧ z = []
Used simplifier rules: prefix-self: ⊦ x ⊑ x;%a: ⊦ (x + y) + z = x + y + z; from specification list% ⊦ x + [] = x; (s)% ⊦ [] + x = x; (s)