Past exam of the model theory course of the University of Oxford / 2011 / 1 / b / i / δ / Solution

No. Interpreting the printed ${\mathbb{Z}}^{⩾}$ as the nonnegative integers, negation is an additive structure automorphism carrying the positive integer one outside that set. The set is therefore not invariant under structure automorphisms and cannot have parameter-free definability. The same argument would apply if the notation were taken to mean the strictly positive integers.