x ⊑ y + a ' ⊦ y + a ' = x, x ⊑ y
Used simplifier rules: postifx-app-03: ⊦ x + y ⊑ x + z ↔ y ⊑ z;%prefix-one-01: ⊦ x ⊑ a ' ↔ x = [] ∨ x = a ';%a: ⊦ (x + y) + z = x + y + z; from specification list% ⊦ a ' ≠ []; (s)