| a ∈ x0 + y, ∀ a0. a0 ∈ a ' + x0 → a0 ∈ y, ∀ y. (∀ a. a ∈ x0 → a ∈ y) → rmdup(x0 + y) = rmdup(y) ⊦ rmdup(x0 + y) = rmdup(y) |
∀ y. (∀ a. a ∈ x0 → a ∈ y) → rmdup(x0 + y) = rmdup(y), ∀ a0. a0 ∈ a ' ∨ a0 ∈ x0 → a0 ∈ y, a ∈ x0 ∨ a ∈ y ⊦ rmdup(x0 + y) = rmdup(y)
Used simplifier rules: a: ⊦ (x + y) + z = x + y + z; from specification list% ⊦ a ∈ x + y ↔ a ∈ x ∨ a ∈ y; (s)