b ' + x + a ' = y + a ' + b ' + z ⊦ y = [], a = b, a ∈ x
Used simplifier rules: Nil: ⊦ [] + x = x;%a: ⊦ (x + y) + z = x + y + z;%c-06: ⊦ a ' + x = b ' + y ↔ a = b ∧ x = y; Used formulas: y = []