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Infinitely growing configurations in Emil Post's tag system problem

Discrete Mathematics 2025-02-27 v2 Computational Complexity

Abstract

Emil Post's tag system problem posed the question of whether or not a tag system {N=3,P(0)=00,P(1)=1101}\{N=3, P(0) = 00, P(1) = 1101\} has a configuration, simulation of which will never halt or end up in a loop. Over the subsequent decades, there were several attempts to find an answer to this question, including a recent study, during which the first 2842^{84} initial configurations were checked. This paper presents a family of configurations of this type in the form of strings AnBCmA^{n} B C^{m} that evolve to An+1BCm+1A^{n+1} B C^{m+1} after a finite number of steps. The proof of this behavior for all non-negative nn and mm is described later in this paper as a finite verification procedure, which is computationally bounded by 20 000 iterations of tag.

Keywords

Cite

@article{arxiv.2105.07529,
  title  = {Infinitely growing configurations in Emil Post's tag system problem},
  author = {Nikita V. Kurilenko},
  journal= {arXiv preprint arXiv:2105.07529},
  year   = {2025}
}

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8 pages, 0 figures

R2 v1 2026-06-24T02:09:37.685Z