| ¬ a0 ∈ a ', ∀ a. x0 \ a ' = x0 ∨ a ∈ x0 ⊦ a0 + (x0 \ a ') = a0 ' + x0, a = a0, a ∈ x0 |
∀ a. x0 \ a ' = x0 ∨ a ∈ x0 ⊦ a = a0, x0 \ a ' = x0, a ∈ x0
Used simplifier rules: in-17: ⊦ a ∈ b ' ↔ a = b; from specification list%a: ⊦ (x + y) + z = x + y + z; from specification list%app-08: ⊦ a ' + x = a ' + y ↔ x = y; from specification list%c: ⊦ a + x = a ' + x; from specification list