| ⊦ (∀ a. a ∈ x → a ∈ z ∨ a ∈ y) ↔ (∀ a. a ∈ x → a ∈ z + y) |
a ∈ x, ∀ a. a ∈ x → a ∈ z ∨ a ∈ y ⊦ a ∈ z, a ∈ y
Used simplifier rules: a: ⊦ (x + y) + z = x + y + z; from specification list%in-append: ⊦ a ∈ x + y ↔ ¬ ¬(a ∈ x ∨ a ∈ y); from specification list