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