| ∀ a, b. a ∈ x0 -l b → a = b ∨ a ∈ x0, a ∈ (a0 + x0) -l b ⊦ a = b, a ∈ a0 + x0 |
a ∈ (a0 ' + x0) -l b, ∀ a, b. a ∈ x0 -l b → a = b ∨ a ∈ x0 ⊦ a = b, a = a0, a ∈ x0
Used simplifier rules: a: ⊦ (x + y) + z = x + y + z; from specification list%in-06: ⊦ ¬ a ∈ b ' + x ↔ a ≠ b ∧ ¬ a ∈ x; from specification list%c: ⊦ a + x = a ' + x; from specification list