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