| y + b ' = y0 + c ' + z ⊦ c = b, c ∈ y |
⊦ 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;%neq: ⊦ ¬ a ∈ x → x ≠ y + a ' + z; Used terms: z