2008.02090
A SOLUTION TO SOME PROBLEMS OF CONWAY AND GUY ON MONOSTABLE POLYHEDRA
Zsolt Lángi
correcthigh confidence
- Category
- Not specified
- Journal tier
- Specialist/Solid
- Processed
- Sep 28, 2025, 12:55 AM
- arXiv Links
- Abstract ↗PDF ↗
Audit review
The paper proves that for any n ≥ 3 and ε > 0 there exists a homogeneous monostable polyhedron with n-fold rotational symmetry arbitrarily close (in Hausdorff distance) to the unit ball, via a general approximation theorem (Theorem 2) that preserves the number and types of equilibrium points under G-invariant polyhedral truncations, and a specific construction of a smooth body K(ε) with one stable and n+1 unstable equilibria used in Theorem 1 . By contrast, the model’s Step 1 takes r(z)^2 = 1 − z^2 + ξ z; but this defines a translated sphere. After recentering at the center of mass (as the model explicitly does), one obtains an exact sphere, for which the boundary is completely degenerate with respect to equilibria, so the claim of “only two axial equilibria and no off-axis equilibria” fails. Subsequent steps rely critically on that false property, and also contradict the cited statement that no body of revolution can be monostable (attributed to Conway) . Hence the model’s argument is untenable, while the paper’s is coherent and complete.
Referee report (LaTeX)
\textbf{Recommendation:} minor revisions
\textbf{Journal Tier:} specialist/solid
\textbf{Justification:}
The paper cleanly settles the existence of n-fold symmetric monostable polyhedra arbitrarily close to the sphere. The main technical tool (approximating smooth bodies by symmetric polyhedra while preserving equilibrium counts) is carefully executed and broadly applicable. A few expository enhancements—particularly explicit parameter bounds and a compact overview of the three-step truncation—would improve readability but do not affect correctness.