The Mathematical Tourist

Dirk Huylebrouck, Editor

Felix Hausdorff in Bonn ROBERT JONES

Does your hometown have any mathematical tourist

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ausdorff remembered and forgotten,’’ reads the cover of The Mathematical Intelligencer, vol. 30 (2008), no. 4. Hausdorff remembered: the brilliant mathematician and author of the groundbreaking Grundzu¨ge der Mengenlehre. Hausdorff forgotten: the once well-known writer, pseudonymously Paul Mongre´. In the ‘‘Years Ago’’ column for that issue [1], Walter Purkert, the director of Hausdorff’s Gesammelte Werke, reunited Hausdorff and Mongre´ in one remarkable man and described his astonishingly rich and varied life. Purkert also described his tragic end: Hausdorff, his wife, and her sister chose suicide in the face of internment in Bonn-Endenich and then Nazi death camps in the east. Mongre´, mon gre´, my choice. Hausdorff’s choice is still largely forgotten. I came across it recently, in the Poppelsdorf Cemetery of Bonn, Germany. It is covered with dust and green moss and small stones placed there by visitors who do remember (Fig. 1).

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attractions such as statues, plaques, graves, the cafe´ where the famous conjecture was made, the desk where the famous initials are scratched, birthplaces, houses, or memorials? Have you encountered a mathematical sight on your travels? If so, we invite you to submit an essay to this column. Be sure to include a picture, a description of its mathematical significance, and either a map or directions so that others may follow in your tracks.

Hausdorff’s Grave The Poppelsdorf Cemetery in Bonn was opened early in the 19th century. Today it is one of several tended by the city department of green surface management (shrubs, grass, trees, etc.). Before the time of Nazi tyranny, the area of Bonn was noted for tolerance, and people of many faiths were interred in Poppelsdorf [2]. There are two paths that a tourist might take through the Poppelsdorf Cemetery to the grave of Felix Hausdorff. One leads through the main entrance, extends past the administration building (Fig. 2a), stops at the grave of another mathematician, Rudolf Lipschitz (Fig. 2b), and then follows an upward path to the grave of Felix Hausdorff.

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Please send all submissions to Mathematical Tourist Editor, Dirk Huylebrouck, Aartshertogstraat 42, 8400 Oostende, Belgium e-mail: [email protected]

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THE MATHEMATICAL INTELLIGENCER Ó 2011 Springer Science+Business Media, LLC

DOI 10.1007/s00283-011-9257-9

Figure 1. The grave of Felix Hausdorff. Placing a stone on a tombstone is an ancient Jewish custom.

Figure 2. (a) The administration building of the Poppelsdorf Cemetery; (b) the grave of Rudolf Lipschitz.

Figure 3. (a) The path from the Baroque church to the grave of Felix Hausdorff; (b) the viewing bench with a view over Bonn.

The other route leads past a small Baroque church (Fig. 3a), then enters the cemetery through a side entrance, and pauses to look out across the city of Bonn from a viewing bench (Fig. 3b). On a clear day, one can see the twin towers of the Cathedral of Cologne. The path leads directly to Hausdorff’s grave.

......................................................................... ROBERT JONES is a student of mathematics and a retired

computer consultant who enjoys listening to Leonard Bernstein discuss musical scales. He acquired a bachelor’s degree in mathematics in 1955 from Michigan State University, and he then worked on the experimental use of an early hard-disc drive, the IBM 305 RAMAC. In 1965 he began working in Germany, where he developed an early virtual memory system. He especially enjoys listening to Leonard Bernstein’s ‘‘Young People’s Concerts.’’ Universitaet Duesseldorf Rurweg 3, D-41844 Wegberg, NRW Germany e-mail: [email protected]

The partially legible inscription on the tombstone reads: Felix Hausdorff Prof. der Mathematik * 8. November 1868 + 26. Januar 1942 Charlotte Hausdorff geb. Goldschmidt * 7. September 1873 + 26. Januar 1942 Edith Pappenheim geb. Goldschmidt * 21. Ma¨rz 1883 + 29. Januar 1942 Lenore Ko¨nig * 1. Februar 1900 + 8. September 1991 Prof. Dr. Arthur Ko¨nig * 13. Oktober 1896 + 24. April 1969. Charlotte: Hausdorff’s wife. Edith Pappenheim: her sister. Felix and Charlotte’s daughter Lenore and her husband Arthur Ko¨nig were buried here later. In a farewell letter to a friend, Hans Wollstein, Hausdorff wrote, ‘‘Auch Endenich ist noch vielleicht das Ende nich!’’ (Hausdorff intentionally omitted the final ‘‘t’’ that the reader expects) and enclosed statements from himself, his wife, and her sister requesting cremation. This explains why their grave is in the part of the Poppelsdorf Cemetery reserved for urns. Ó 2011 Springer Science+Business Media, LLC, Volume 34, Number 1, 2012

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Figure 4. (a) The flagstones in Hausdorff Street; (b) the Hausdorff story on a street sign.

Figure 7. Entrance of the Hausdorff Center for Mathematics. Figure 5. Hausdorffstrasse 61, Bonn.

Figure 6. (a) Plaque in memory of Otto Toeplitz; (b) Plaque in memory of Felix Hausdorff.

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Figure 8. (a) The Cloister Endenich in the Bonn City Museum; (b) the entrance to the monastery as it is today.

Hausdorff’s House In Bonn, Felix Hausdorff lived in what was then Hindenburgstrasse 61. The street was later renovated and renamed in his honor, with the numbering retained. Today the story of his life and death, in abbreviated form, is related in brass flagstones (Fig. 4a) embedded in the sidewalk in front of his house. It is also told, in slightly less abbreviated form, on the street sign on the block in which his house still stands (Fig. 4b): Professor Doctor Felix Hausdorff, born 1868, Jewish Mathematician in Bonn, driven to suicide on the 26th of January, 1942 by the Nazi regime. Among his many talents, Hausdorff was an accomplished pianist. Today his house (Fig. 5) is alive with music once again. The present owners, Georg Brinkmann and Vanessa Vromans, experts on klezmer music, argue that music is mathematics, writ by scales.

The Former Mathematical Institute The former Mathematical Institute building is on Wegeler Street. In the entrance hallway there are two plaques engraved in granite (Figs. 6a,b). The plaque on the left reads (in translation), ‘‘To the memory of Otto Toeplitz, 1.8.1881 – 15.2.1940, mathematician, teacher and colleague, by the Nazis demeaned, humiliated and exiled, because he was a Jew.’’ On the other side of the eerily silent hallway, we read, ‘‘At this university, 1921 – 1935, the mathematician Felix Hausdorff, 8.11.1868 – 26.1.1942, was active. He was driven by the Nazis to his death, because he was a Jew. With him we honor all victims of tyranny. Never again the rule of violence and war!’’ The imposing Hausdorff Center for Mathematics, at Endenicher Allee 62 (Fig. 7), is an easy stroll from the Hausdorff Institute of Mathematics. The Hausdorff Edition [1] has its offices in this building, and there is a treasure trove from the legacy and collected writings of Felix Hausdorff.

proceed there prompted Hausdorff’s suicide. Endenich is a part of the city of Bonn, and it is not far from the center. After the war, the ‘‘Internierungslager’’ again became a cloister. It can be visited today (Fig. 8b).

The Hausdorff Family Today There is none. Walter Purkert answered my inquiry, There are unfortunately no longer any descendants of Felix Hausdorff, and we also have been unable to find any living relatives. His two sisters married and lived with their families in Prague. As far as we are able to determine, from Czechoslovakian archives, both families fell victim to the Nazis. We do not know whether some of the children of these families may have succeeded in fleeing. One son of the Brandeis family was definitely murdered. Mrs. Ko¨nig had two sons, Felix born in 1927, and Hermann born in 1929. Hermann suffered from a metabolic disorder which leads, with normal diet, to mental retardation (today all babies are tested and it is possible, with dietary restrictions, to prevent the development of the consequences of this disorder). Hermann survived the Nazi era in a children’s home. He lived for several years in a medical care home in Wiesloch (near Heidelberg). The nurses there told us that he had the mentality of a four-year-old. We do not know whether he is still alive. Felix died with his wife in an auto accident. They did not have children. That is the entire sad story. ACKNOWLEDGMENTS

I would like to thank Georg Brinkmann and Vanessa Vromans for their interest, for their assistance, and for giving the Hausdorff home new life. I am also grateful to Walter Purkert for patiently answering my many questions.

The Cloister of Endenich

Web Links

In the Bonn City Museum you will find a photograph of a Benedictine monastery in Endenich, the ‘‘cloister [that] became a concentration camp’’ (Fig. 8a). The order to

Map image showing the baroque church, called the Kreuzbergkirche, at Stationsweg 21, near the grave of Felix Hausdorff: Ó 2011 Springer Science+Business Media, LLC, Volume 34, Number 1, 2012

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http://wiki.worldflicks.org/kreuzbergkirche.html#coords =%2850.71524128335446,7.081359028816223%29&z=18. Shifting this map upward, near the oval-shaped path near the center of the picture, one can see the location of Felix Hausdorff’s grave. Map picture centered on the grave of Felix Hausdorff: http://wiki.worldflicks.org/kreuzbergkirche.html#coords=% 2850.71642329060522,7.082592844963074%29&z=18 Germany / North-Rhine-Westphalia / Poppelsdorf (today Bonn-Poppelsdorf): http://www.porcelainmarksandmore.com/northrhine/pop pelsdorf_1/00.php

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http://www.nu-klezmer.de http://www.people.umass.edu/gmhwww/382/pdf/12-music% 20scales.pdf

REFERENCES

[1] Purkert, Walter, ‘‘The Double Life of Felix Hausdorff/Paul Mongre´,’’ The Mathematical Intelligencer, 30(4), Winter 2008, 36-50. [2] Bajor, Stefan, Archives in Stone, Jewish Life and Jewish Cemeteries in North-Rhine-Westphalia [Archiv aus Stein, Ju¨disches Leben und ju¨dische Friedho¨fe in Nordrhein-Westfalen], Asso Verlag, Oberhausen, Germany, 2005.