Equations over sets of integers with addition only

Systems of equations of the form $X=Y+Z$ and $X=C$ are considered, in which the unknowns are sets of integers, the plus operator denotes element-wise sum of sets, and C is an ultimately periodic constant. For natural numbers, such equations are equivalent to language equations over a one-symbol alphabet using concatenation and regular constants. It is shown that such systems are computationally universal: for every recursive (r.e., co-r.e.) set $S\subseteq \mathbb{N}$ there exists a system with a unique (least, greatest) solution containing a component T with $S=\{n|16n+13\in T\}$. Testing solution existence for these equations is ${\mathrm{\Pi }}_1^0$-complete, solution uniqueness is ${\mathrm{\Pi }}_2^0$-complete, and finiteness of the set of solutions is ${\mathrm{\Sigma }}_3^0$-complete. A similar construction for integers represents any hyper-arithmetical set $S\subseteq \mathbb{Z}$ by a set $T\subseteq \mathbb{Z}$ satisfying $S=\{n|16n\in T\}$, whereas testing solution existence is ${\mathrm{\Sigma }}_1^1$-complete.