Equichordal point problem: Difference between revisions

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The theorem solves the Equichordal Point Problem of Fujiwara, originally posed in 1916. The problem was rediscovered in 1917 by Wilhelm Blaschke, Rothe and Weizenböck.

The Theorem

There is no $C$ be a Jordan curve with two equichordal points, with respect to which the curve $C$ would be star-shaped. In particular, there is no convex and closed curve with two equichordal points.

The Published Proof

The proof was published in the hard to read article ^[1] There is also easy to read research announcement ^[2], but it only hints atthe ideas used in the proof.

The History of the Problem

In 1916 Fujiwara proved that no convex curves with three equichordal points exist.
In 1923 S\"uss showed certain symmetries and uniqueness of the curve, if it existed.
In 1953 G. A. Dirac showed some explicit bounds on the curve, if it existed.
In 1958 Wirsing showed that the curve, if it exists, must be an analytic curve. In this deep paper, he correctly identified the problem as perturbation problem beyond all orders.
In 1966 Ehrhart proved that there are no equichordal curves with eccentricities > 0.5.
In 1988 Michelacci proved that there are no equichordal curves with eccentricities > .33. The proof is mildly computer-assisted.
In 1992 Sh\"afke and Volkmer showed that there is at most a finite number of values of eccentricity for which the curve may exist. They outlined a feasible strategy for a computer-assisted proof.
In 1996 Rychlik fully solved the problem. The proof does not use a computer.

References

^ Marek R. Rychlik, A complete solution to the equichordal point problem of Fujiwara, Blaschke, Rothe and Weizenböck, Inventiones Mathematicae, 1997, Volume 129, Number 1, Pages 141-212.
^ [http://www.mpim-bonn.mpg.de/era-mirror/1996-03-002/1996-03-002.html Marek Rychlik, The Equichordal Point Problem, Electronic Research Announcements of the AMS, 1996, pages 108-123]

[The_Proof-1] Marek R. Rychlik, A complete solution to the equichordal point problem of Fujiwara, Blaschke, Rothe and Weizenböck, Inventiones Mathematicae, 1997, Volume 129, Number 1, Pages 141-212.

[The_Announcement-2] [http://www.mpim-bonn.mpg.de/era-mirror/1996-03-002/1996-03-002.html Marek Rychlik, The Equichordal Point Problem, Electronic Research Announcements of the AMS, 1996, pages 108-123]

[1]

[2]

@@ Line 9: / Line 9: @@
 [[Marek Rychlik]], The Equichordal Point Problem, Electronic Research Announcements of the AMS,
 , pages 108-123]</ref>, but it only hints atthe ideas used in the proof.
+== The History of the Problem ==
+# In 1916 Fujiwara proved that no convex curves with three equichordal points exist.
+# In 1923 S\"uss showed certain symmetries and uniqueness of the curve, if it existed.
+# In 1953 G. A. Dirac  showed some explicit bounds on the curve, if it existed.
+# In 1958 Wirsing showed that the curve, if it exists, must be an [[analytic curve]]. In this deep paper, he correctly identified the problem as [[perturbation problem beyond all orders]].
+# In 1966 Ehrhart proved that there are no equichordal curves with eccentricities > 0.5.
+# In 1988 Michelacci proved that  there are no equichordal curves with eccentricities > .33. The proof is mildly computer-assisted.
+# In 1992 Sh\"afke and Volkmer  showed that there is at most a finite number of values of eccentricity for which the curve may exist. They outlined a feasible strategy for a computer-assisted proof.
+# In 1996    Rychlik fully solved the problem. The proof does not use a computer.
 == References ==