| x = y0 + a0 ', a ∈ x ⊦ a = a0, x = [], ∃ y, z. x = y + a ' + z ∧ z ≠ [] |
a ∈ y0 ⊦ a = a0, ∃ y, z. y0 + a0 ' = y + a ' + z ∧ z ≠ []
Used simplifier rules: ⊦ a ∈ b ' ↔ a = b; (s)% ⊦ a ∈ x + y ↔ a ∈ x ∨ a ∈ y; (s)%a: ⊦ (x + y) + z = x + y + z; from specification list% ⊦ x + a ' ≠ []; (s)