| x + a ' = y + b ' + z ⊦ a = b, ∃ z0. z = z0 + a ' |
⊦ x ≠ [] → (∃ y, a. x = y + a ')
Used simplifier rules: app: ⊦ x + [] = x;%a: ⊦ (x + y) + z = x + y + z;%app-06: ⊦ x + a ' = y + b ' ↔ x = y ∧ a = b;%in-15: ⊦ x + a ' = y → a ∈ y;%e-02: ⊦ x + a ' ≠ [];%in-append: ⊦ a ∈ x + y ↔ ¬ ¬(a ∈ x ∨ a ∈ y);%in-17: ⊦ a ∈ b ' ↔ a = b; Used terms: z