2106.10687
Factoring Strongly Irreducible Group Shift Actions onto Full Shifts of Lower Entropy
Dawid Huczek, Sebastian Kopacz
correcthigh confidence
- Category
- Not specified
- Journal tier
- Specialist/Solid
- Processed
- Sep 28, 2025, 12:56 AM
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Audit review
The uploaded paper proves the factor theorem under the stated hypotheses using subsystem entropy density, a carefully constructed marker block plus tiling (Theorem 4.1), and a quasitiling that factors locally onto an exact tiling via the comparison property (Theorems 2.11–2.13). It then defines a precise sliding block code and proves surjectivity by a controlled pasting inside D-interiors, coding on SD \ D(K ∪ K*) and using an auxiliary map ψ. The candidate solution mirrors this blueprint but makes a critical, self-contradictory choice of a set P with KP ⊂ U while also requiring P ∩ U = ∅ even though e ∈ K, which cannot hold; it also omits the essential K* and ψ components and codes on entire tiles rather than on the protected interior subset. These gaps undermine the correctness of its sliding block code and surjectivity argument.
Referee report (LaTeX)
\textbf{Recommendation:} minor revisions
\textbf{Journal Tier:} specialist/solid
\textbf{Justification:}
This work consolidates and extends techniques in the amenable-group symbolic dynamics toolkit to prove a clean and useful factor theorem below entropy for strongly irreducible, aperiodic shifts under the comparison property. The strategy is sound, dependencies are correctly cited, and the proof handles the delicate locality and tiling issues with care. A few expository improvements (parameter bookkeeping, intuitive explanation of the marker construction, and a brief cardinality estimate for the coding domain) would make the paper more accessible, but the results appear correct and of genuine interest to specialists.