x + a ' + y = b ' ⊦ x = [] ∧ a = b ∧ y = []
Used simplifier rules: Nil: ⊦ [] + x = x;%app: ⊦ x + [] = x;%a: ⊦ (x + y) + z = x + y + z;%c-04: ⊦ a ' = b ' ↔ a = b;