2102.02419
Two new families of finitely generated simple groups of homeomorphisms of the real line
James Hyde, Yash Lodha, Cristóbal Rivas
correcthigh confidence
- Category
- math.DS
- Journal tier
- Specialist/Solid
- Processed
- Sep 28, 2025, 12:55 AM
- arXiv Links
- Abstract ↗PDF ↗
Audit review
The paper’s arguments for both families are correct and complete. The candidate solution substantially follows the paper’s structure for the hard steps (repetitivity/regularization/advancing for G_λ and proximality/special elements/no-backtracking for H_n). However, it makes a critical error in Task A: it conflates Thompson’s group on the circle with its lifts to the line. It asserts T and T_λ (the lifts) are perfect/simple and uses this to deduce G_λ is perfect and that any nontrivial element of N ∩ T normally generates T inside T. In the paper, simplicity of the lifts is not true; instead, the needed fact is that any noncentral element of the lift normally generates the lift (used explicitly in the proof) . Because the model’s justification hinges on a false claim, its proof of simplicity for G_λ is invalid as written, even though the intended path mirrors the paper’s correct proof via Proposition 2.2.1 and the commutator trick . Task B matches the paper closely (simplicity, finite generation, and faithful lift/left orderability) , but an unnecessary claim about preserving the “marked isomorphism type” of fast n-rings goes beyond what is cited and is not needed.
Referee report (LaTeX)
\textbf{Recommendation:} reject
\textbf{Journal Tier:} specialist/solid
\textbf{Justification:}
The write-up mirrors the correct structure of the paper for both families and cites the right technical lemmata. However, it contains a central error in Task A: it treats the lifts T and T\_λ as simple/perfect and uses this to justify key normal-closure steps. The paper carefully avoids this and instead uses the fact that any noncentral element in the lift normally generates the entire lift. Because this mistake undermines the proof of simplicity for G\_λ, the submission is incorrect as written.