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2006.04783

DISTINGUISHING ENDPOINT SETS FROM ERDŐS SPACE

David S. Lipham

correcthigh confidence
Category
math.DS
Journal tier
Specialist/Solid
Processed
Sep 28, 2025, 12:55 AM

Audit review

The paper proves that the escaping endpoint set Ė(f) for f(z)=e^z−1 is not homeomorphic to Q×X for any space X via a brush-model plus a topological lemma and an explicit simple-closed-curve construction around endpoints; the argument is coherent and complete in the provided text (see the statement of Theorem 1 and its proof outline and completion) . By contrast, the model’s proof hinges on unproven—and likely false—claims: (i) that the escaping endpoints Ė(f) are homeomorphic to an open subset of Z^N (hence Polish/Baire), and (ii) that the address–endpoint map is a homeomorphism on the subspace of addresses with positive minimal potential. The paper’s brush model does not imply these topological identifications; in particular, the set Σ_fast={s:t_s>0} need not be open in the product topology on Z^N, and “escaping endpoint = t_s>0” is not justified. Consequently, the model’s Baire-vs-meagre argument lacks the required foundations.

Referee report (LaTeX)

\textbf{Recommendation:} minor revisions

\textbf{Journal Tier:} specialist/solid

\textbf{Justification:}

A concise and well-motivated note that cleanly separates the topology of escaping endpoints from the class Q×X by an elegant geometric argument in the brush model. The proof is correct as written and yields additional insight (a simple closed curve separating each escaping endpoint from infinity, and path-connectedness of the complement). A few minor clarifications in the construction could further improve readability.