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Today marks eighty years since the passing of Julius Wolff in Bergen-Belsen concentration camp. Wolff served as a professor at Utrecht ľ¹Ï¸£ÀûÓ°ÊÓ from 1922 to 1941 and was internationally recognized for his contributions to the field of mathematics - some of which remain relevant today. Despite the efforts of colleagues and others to protect him, Wolff, along with his wife and youngest son, was deported via Camp Westerbork to Germany, where he died. Utrecht emeritus professor Jan van Maanen made an extensive study of Julius Wolff's life and work.

‘Dr. Wolff has [] shown a remarkable intuition in the analytical-mathematical field. He has repeatedly succeeded in finding an answer to questions which famous mathematicians have investigated without reaching a solution. [] Dr. Wolff [is] not only [sic] specialised in the theory of functions, but [] also well versed in other fields of mathematics. [] Finally, we note, that Dr Wolff is an excellent akademic lecturer.’

With the above words, the Faculty of Mathematics and Physics of Utrecht ľ¹Ï¸£ÀûÓ°ÊÓ nominated Julius Wolff in 1922 when a position became vacant. He was then a professor at the ľ¹Ï¸£ÀûÓ°ÊÓ of Groningen but accepted and held his inaugural lecture on 16 October.

Versatile academic

Van Maanen's work shows that Wolff was a particularly versatile academic. He was an experienced, passionate lecturer who was also closely involved with his PhD candidates. His research spanned multiple fields, including analysis and function theory – his primary focus – as well as geometry, mathematical foundations and the connection with physics.

Wolff’s publications reached a global audience; he wrote in French, German, and English, choosing to publish in prestigious international journals. Beyond academia, he was actively involved in university administration, serving as faculty chairman, and contributed as a statistical consultant for the insurance company Olveh, a predecessor of Aegon.

Theorem engraved

One of Julius Wolff’s most significant contributions to mathematics is the Denjoy–Wolff theorem. While Jan van Maanen does not delve deeply into its content, he refers to an  (in Dutch). French mathematician Arnaud Denjoy and Wolff independently discovered the theorem and published their findings in 1926. The theorem plays a key role in complex analysis (the study of complex functions) and dynamical systems, which have wide applications in fields like applied mathematics.

The theorem has been permanently honoured in the library of Utrecht ľ¹Ï¸£ÀûÓ°ÊÓ’s Mathematical Institute—engraved on the lunch table alongside other milestones of Utrecht’s mathematical legacy. Another major contribution by Wolff is his extension of the Schwarz lemma, now known as the Schwarz–Wolff lemma.

My lectures went quite well, but now there is stagnation because the audience is often ill or prevented from attending

Increasing restrictions

Under pressure from the occupying forces, Utrecht ľ¹Ï¸£ÀûÓ°ÊÓ dismissed Julius Wolff from his position on 23 November 1940. His official resignation followed a few months later. However, as Jan van Maanen’s research shows, this did not stop Wolff from working. Despite increasing restrictions and forced removals—such as Jews being banned from the Mathematics Library—he continued to publish. He also held weekly colloquiums with German mathematician Otto Blumenthal, discussing their own research and recent mathematical developments.

Even after being deported to Westerbork, Wolff persisted in holding mathematics meetings. However, over time, these gatherings became increasingly difficult. "My lectures went quite well, but now there is stagnation because the audience is often ill or prevented from attending," he wrote in a letter to his successor, Dr. L.W. Nieland.

Unpleasant visits

Using correspondence, Van Maanen illustrates Wolff’s relentless efforts to secure protected status for himself and his family. Among those advocating on his behalf was Rector Magnificus Louis van Vuuren, who tirelessly pleaded Wolff’s case with both Dutch authorities and the occupying forces. Wolff expressed his deep gratitude in a letter to Van Vuuren, writing, "Thank you very much for everything you did for my sake, especially for the unpleasant visits you made."

Arrest

Despite his efforts, Wolff and his wife were arrested on 8 March 1943 and sent to Westerbork. After two weeks, they secured a transfer to Barneveld, where two homes had been designated for Jews with protected status. However, just four months later, the occupying forces ordered the entire group back to Westerbork. On 13 September 1944, Wolff, his wife, and their youngest son were deported to Bergen-Belsen. According to his death certificate, Wolff suffered cardiac arrest on 8 February 1945. His wife and son died shortly afterward.

Wolff's daughter, Lenie, survived the war by going into hiding. His eldest son, Louis, had passed away in 1940.