| a0 ∈ y, a ∈ y, a ∈ (a0 ' + x0) \ y, ∀ a1, y0. ¬ a1 ∈ x0 \ y0 ∨ ¬ a1 ∈ y0 ⊦ |
a0 ∈ y, a ∈ y, a ∈ x0 \ y, ∀ a1, y0. ¬ a1 ∈ x0 \ y0 ∨ ¬ a1 ∈ y0 ⊦
Used simplifier rules: diff-y: ⊦ a ∈ y → (a ' + x) \ y = x \ y;%a: ⊦ (x + y) + z = x + y + z; from specification list