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