### Abstract

This article explains why a paper by Heinz G. Helfenstein entitled Ovals with equichordal points, J. London Math. Soc. 31 (1956), 54-57, is incorrect. We point out a computational error which renders his conclusions invalid. More importantly, we explain that the method presented there cannot be used to solve the equichordal point problem. Today, there is a solution to the problem: Marek R. Rychlik, A complete solution to the equichordal point problem of Fujiwara, Blaschke, Rothe and Weizenböck, Inventiones Mathematicae 129 (1997), 141-212. However, some mathematicians still point to Helfenstein's paper as a plausible path to a simpler solution. We show that Helfenstein's method cannot be salvaged. The fact that Helfenstein's argument is not correct was known to Wirsing, but he did not explicitly point out the error. This article points out the error and the reasons for the failure of Helfenstein's approach in an accessible, and hopefully enjoyable way.

Original language | English (US) |
---|---|

Pages (from-to) | 499-521 |

Number of pages | 23 |

Journal | New York Journal of Mathematics |

Volume | 18 |

State | Published - Jun 28 2012 |

### Fingerprint

### Keywords

- Convex geometry
- Equichordal point problem

### ASJC Scopus subject areas

- Mathematics(all)

### Cite this

**Why is Helfenstein's claim about equichordal points false?** / Rychlik, Marek R.

Research output: Contribution to journal › Article

*New York Journal of Mathematics*, vol. 18, pp. 499-521.

}

TY - JOUR

T1 - Why is Helfenstein's claim about equichordal points false?

AU - Rychlik, Marek R

PY - 2012/6/28

Y1 - 2012/6/28

N2 - This article explains why a paper by Heinz G. Helfenstein entitled Ovals with equichordal points, J. London Math. Soc. 31 (1956), 54-57, is incorrect. We point out a computational error which renders his conclusions invalid. More importantly, we explain that the method presented there cannot be used to solve the equichordal point problem. Today, there is a solution to the problem: Marek R. Rychlik, A complete solution to the equichordal point problem of Fujiwara, Blaschke, Rothe and Weizenböck, Inventiones Mathematicae 129 (1997), 141-212. However, some mathematicians still point to Helfenstein's paper as a plausible path to a simpler solution. We show that Helfenstein's method cannot be salvaged. The fact that Helfenstein's argument is not correct was known to Wirsing, but he did not explicitly point out the error. This article points out the error and the reasons for the failure of Helfenstein's approach in an accessible, and hopefully enjoyable way.

AB - This article explains why a paper by Heinz G. Helfenstein entitled Ovals with equichordal points, J. London Math. Soc. 31 (1956), 54-57, is incorrect. We point out a computational error which renders his conclusions invalid. More importantly, we explain that the method presented there cannot be used to solve the equichordal point problem. Today, there is a solution to the problem: Marek R. Rychlik, A complete solution to the equichordal point problem of Fujiwara, Blaschke, Rothe and Weizenböck, Inventiones Mathematicae 129 (1997), 141-212. However, some mathematicians still point to Helfenstein's paper as a plausible path to a simpler solution. We show that Helfenstein's method cannot be salvaged. The fact that Helfenstein's argument is not correct was known to Wirsing, but he did not explicitly point out the error. This article points out the error and the reasons for the failure of Helfenstein's approach in an accessible, and hopefully enjoyable way.

KW - Convex geometry

KW - Equichordal point problem

UR - http://www.scopus.com/inward/record.url?scp=84875462545&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=84875462545&partnerID=8YFLogxK

M3 - Article

AN - SCOPUS:84875462545

VL - 18

SP - 499

EP - 521

JO - New York Journal of Mathematics

JF - New York Journal of Mathematics

SN - 1076-9803

ER -