English

Additive systems for $\mathbb{Z}$ are undecidable

Combinatorics 2026-04-14 v2 Logic in Computer Science

Abstract

What are the collections of sets AiZ{A}_i\subset\mathbb{Z} such that any nZn\in\mathbb{Z} has exactly one representation as n=a0+a1+n=a_0+a_1+\dotsb with aiAia_i\in{A}_i? The answer for N0\mathbb{N}_0 instead of Z\mathbb{Z} is given by a theorem of de Bruijn. We describe a family of natural candidate collections for Z\mathbb{Z}, which we call canonical collections. Translating the problem into the language of dynamical systems, we show that the question of whether the sumset of a canonical collection covers the entire Z\mathbb{Z} is difficult: specifically, there is a collection for which this question is equivalent to the Collatz conjecture, and there is a well-behaved family of collections for which this question is equivalent to the universal halting problem for Fractran and is therefore undecidable.

Keywords

Cite

@article{arxiv.2508.17285,
  title  = {Additive systems for $\mathbb{Z}$ are undecidable},
  author = {Andrei Zabolotskii},
  journal= {arXiv preprint arXiv:2508.17285},
  year   = {2026}
}

Comments

11 pages

R2 v1 2026-07-01T05:03:21.052Z