One of the founders of modern topology was also a writer, poet, and philosopher who published under the name Paul Mongera. His life ranged between Germany's scientific and cultural elite and exclusion and persecution due to his Jewishness under the Nazi regime.
The great German mathematician Felix Hausdorff Born on November 8, 1868 in Breslau, now Wrocław, Poland, to a wealthy Jewish family. His father was a textile merchant, and when Hausdorf was a toddler the family moved to Leipzig. There he was educated and received a significant part of his academic training. Already at school his broad interests were evident: alongside theMathematics He was drawn to literature, philosophy, and especially music. For a time he hoped to become a composer, but under the influence of his parents he abandoned the plan and turned to studying mathematics and astronomy.
Hausdorff studied at the universities of Leipzig, Freiburg, and Berlin. In 1891, he received a doctorate from the University of Leipzig for research on the refraction of light in the atmosphere. Four years later, he completed his habilitation – the qualification that allowed him to teach at the university – also in the field of astronomy and optics. In 1895, he began teaching at Leipzig as a private lecturer, and from 1901 he served as an extraordinary professor there.
In 1910 he was appointed associate professor atUniversity of BonnThree years later he received a full professorship at the University of Greifswald, and in 1921 he returned to Bonn, where he continued to teach and research until 1935.
The life of Paul Mongra
In parallel with his scientific work, Hausdorff led an extensive literary and philosophical career under the pseudonym Paul Mongra – Paul Mongré. The name was a play on the French expression at my request, which means “according to my will” or “according to my taste.”
The pseudonym allowed him to express a completely different side to the restrained and precise persona he presented at university. As Felix Hausdorff, he was a rigorous mathematician; as Paul Mongraë, he wrote with irony, criticized social and religious conventions, and dealt with love, art, personal freedom, and man's place in the world.
He belonged to a circle of writers, artists and musicians, including the playwright Frank Wedkind, the composer Max Reger and the artist Max Klinger. Between 1897 and 1904 he published most of his literary and philosophical work: the Book of Aphorisms Sant' Ilario: Gedanken aus der Landschaft Zarathustras, the epistemological connection Das Chaos in kosmischer Auslese, the book of songs Ecstasy and numerous articles in Germany's leading literary journals.
In 1904 he published the farce The doctor of his honor – Freely translated, “The Doctor of His Honor.” The play was his greatest literary success and was performed hundreds of times in dozens of cities. At one time, not all of his acquaintances from the mathematical world knew that Professor Hausdorff and the writer Mongra were the same person.
These were not two completely separate lives. Freedom of thought, skepticism towards conventions and a tendency to reexamine basic concepts characterized both his literary writing and his mathematics. In mathematics too, he was not content with solving existing problems, but sought to reformulate the language in which spaces, order, continuity and dimension are described.
One of the founders of modern topology
In 1914, Hausdorff published his great book Basics of set theory – “Fundamentals תורת הקבוצות". The book was much more than a textbook on set theory. It created a general and systematic framework for the study of abstract spaces and was one of the works that shaped theTopology As an independent mathematical field.
Topology studies properties of spaces that are preserved when they are stretched, shrunk, or distorted continuously, without tearing or pasting. One of the fundamental concepts in the field is now called Hausdorff space: A space in which any two distinct points can be separated by non-overlapping neighborhoods. This condition seems abstract, but it helps ensure that convergence and limits behave unambiguously.
Hausdorff also contributed to the theory of ordered sets, measure theory, functional analysis, probability theory, and algebra. He studied the power of Borel groups and developed tools for measuring complex groups in spaces that do not have to be lines, surfaces, or regular bodies.
From here they grew Hausdorff measure וHausdorff dimensionUnlike the usual dimension – zero for a point, one for a line, two for a surface and three for a solid – the Hausdorff dimension can also be a non-integer. This concept later became central to the study of Fractals, dynamical systems, chaos, geometry and signal analysis.
Hausdorff's name is now associated with a long list of concepts and theorems: Hausdorff space, Hausdorff distance, Hausdorff measure, Hausdorff dimension, Hausdorff's maximum principle, Hausdorff's moment problem, and the Hausdorff–Young inequality. His contributions also extended to algebra, probability, and actuarial mathematics.
From the academic elite to exclusion
The Nazis' rise to power in 1933 gradually changed his life. The regime began to expel Jewish faculty members from universities and to distance them from public life. Hausdorff remained at the University of Bonn until 1935, when he was given emeritus status. Even after he stopped teaching, he continued to work and publish research, mainly in mathematical journals outside Germany. Between 1933 and 1938, he published seven more articles, most of them in Polish journals.
The persecution intensified after the November 1938 pogrom. Hausdorff tried to find a way to emigrate to the United States. Important mathematicians including Richard Courant, Hermann Weyl, and John von Neumann tried to help, emphasizing that despite his age he continued to create first-rate mathematics. The efforts were unsuccessful, partly because no position or research fellowship was found for him that would allow him to emigrate.
A German identity that the regime denied
The story of Felix Hausdorff is a story of several identities that existed side by side. He was a mathematician and a writer, a scientist and a spiritual man, a man who lived in a world of precise proofs but also in a world of poetry, philosophy, and theater.
He was also a Jew of German culture. Like many educated and assimilated Jews of his time, he saw his world in German language, science, and culture. He was a member of Germany's academic elite and made a fundamental contribution to its scientific standing. But the Nazi regime suddenly nullified his achievements, his status, and his sense of belonging, classifying him solely by his origin.
Precisely because he was so rooted in German culture, the exclusion was a personal and cultural disaster for him. A man who for decades had been a respected professor, a well-known writer, and an active participant in intellectual life found himself isolated and threatened by the country he considered his homeland.
His legacy, however, survived the regime that persecuted him. Modern topology, measure theory, and the study of fractals still use his ideas today. The University of Bonn, from which he was expelled, established the Hausdorff Center for Mathematics in his name. His mathematical, literary, and philosophical writings have been collected and published in a large-scale scientific edition.
The tragic death
Felix Hausdorff was not just a multidisciplinary mathematician or a writer hiding behind a pen name. Both sides were expressions of the same personality: a man who sought to test the limits of thought, to break free from conventions, and to create a new language – sometimes through equations and definitions, and sometimes through aphorisms, poetry, and theater. In January 1942, Hausdorff, his wife Charlotte, and his sister-in-law Edith were ordered to report for transfer to the Bandenich concentration camp near Bonn, a stop that could have led to deportation to camps in the East. Hausdorf understood the meaning of the order well.
In a farewell letter he wrote on January 25, 1942, he stated that he and his family had decided to “solve their problem,” described what had been done to the Jews in the preceding months as an unbearable situation, asked his friends to forgive them, and wished them a better future. The following night, Hausdorff, his wife, and his sister-in-law committed suicide. On the morning of January 26, all three were found dead.
His death was not just the personal end of a persecuted mathematician. It illustrated the complete collapse of his world: a man who saw himself as a German, who was part of his country's scientific and cultural elite and whose work contributed to its prestige, became, in the eyes of the Nazi state, a foreigner without rights, destined for deportation and extermination.
More on the subject on the science website
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