15/06/2026
Today, a “Stolperstein” was laid at the former residence of Otto Toeplitz, at Wittelsbacher Ring 1. Two of Otto Toeplitz’s grandchildren, Tamar Vital and Ronnie Toeplitz, were in attendance; they had traveled from Israel especially for the occasion. In addition, many students from the nearby Ernst-Moritz-Arndt-Gymnasium and numerous professors and students from the Hausdorff Center for Mathematics took part.
A Stolperstein (“stumbling block”) is a ten-centimeter cube bearing a brass plate inscribed with the name and dates of birth and death of victims of N**i extermination or persecution. The Stolpersteine project aims to commemorate individuals at the last place they freely chose to live, work, or study before they fell victim to N**i terror, forced euthanasia, eugenics, or deportation to a concentration or extermination camp, or escaped persecution through emigration or su***de.
Special thanks go to the students of the Ernst-Moritz-Arndt-Gymnasium (which will be renamed the Felix-Hausdorff-Gymnasium in a few months). In May 2024, students there published a special edition of the school newspaper titled “Stolpersteine – Frieden durch Erinnerung.” The editorial team researched biographies, reviewed historical sources, conducted interviews with experts, and brought to light the fates of people who lived in Bonn and were disenfranchised, displaced, or murdered as a result of N**i persecution. This journalistic commitment eventually led to something more: the student editorial team wanted not only to remember, but also to make their own contribution to the culture of remembrance in our city. Through the sale of the special edition and additional donations, a total of 2,520 euros was raised. This sum will now be used to fund 22 Stolpersteine, which will be laid today and in three days’ time in the Bonn city area.
Otto Toeplitz was born in Breslau in 1881, the son of mathematician Emil Toeplitz and his wife Pauline. He studied mathematics in Berlin and Breslau, where he earned his doctorate in 1905 with a dissertation on algebraic geometry. In 1907, he qualified as a professor in Göttingen, became a full professor in Kiel in 1920, and was appointed to Bonn in 1928. In Bonn, he was friends with Felix Hausdorff. After the National Socialists came to power, everything changed in the Toeplitz family’s life as well. Otto Toeplitz was forced into retirement in 1935 at the age of 53. The family had to leave their home on Wittelsbacher Ring and move in 1936 to a small apartment in the house of the widow of a Jewish colleague at 102 Koblenzer Straße. In 1938, Otto Toeplitz had been invited to give a lecture at the University of Jerusalem in order to secure a position there. Prior to this, the Gestapo had summoned him and pressured him to return to Bonn. After the November pogrom, he received a renewed job offer from the University of Jerusalem. Consequently, the Toeplitz couple left Bonn in 1939 and traveled via Switzerland to Jerusalem. Otto Toeplitz soon fell ill with typhus and died in 1940.
Following his dissertation, his main area of research became the theory of linear operators (which he still treated as infinite matrices) in normed spaces. Today, this field is part of functional analysis. Furthermore, Toeplitz made significant contributions to function theory. His conjecture that a square can be inscribed in every closed Jordan curve has to date neither been proven nor refuted (Toeplitz conjecture). The conjecture holds for a class of special Jordan curves. Three of his works in functional analysis have gained particular significance and should therefore be mentioned separately here. For the five-year period 1988–1992, Peter Lax (Courant Institute, New York) analyzed the data from the “Mathematical Reviews” and found that 394 papers from this period mention Toeplitz in the title and that Toeplitz is cited in the text of 1,191 papers. The vast majority of all these references pertain to Toeplitz’s nearly two-page article “On the Fourier Expansion of Positive Functions” from 1911. In this article, Toeplitz introduced the matrices that are now named after him and used these matrices to solve a problem posed by Constantin Carathéodory (1873–1950). The theory of these matrices and their generalizations found application in various branches of mathematics such as Fourier analysis, particle differential equations, time series analysis, random walks, and the development of fast algorithms, but also far beyond mathematics into crystallography, statistical mechanics, quantum mechanics, and quantum chromodynamics.
