⊦ dups(x) ↔ (∃ a, x0, y, z. x = x0 + (a + (y + (a + z))))
⊦ dups(a ' + x) ↔ (∃ a, x0, y, z. x = x0 + (a + (y + (a + z)))), a ∈ x
Used terms: x