**Zassenhaus** did important work on Group Theory and Lie algebras.

- Julius Zassenhaus was a historian who was the principal of a girls' gymnasium.
- After graduating from this school, Hans entered the University of Hamburg in the autumn of 1930.
- Zassenhaus studied for his doctorate under Artin's supervision.
- During this time he proved the Zassenhaus (butterfly) lemma, a beautiful result on subgroups which can be used to give a simple, and very beautiful, proof of the Jordan-Hölder theorem.
- Despite all the turmoil in his life, Hans Zassenhaus completed his doctoral dissertation Kennzeichnung endlicher linearer Gruppen als Permutationsgruppen Ⓣ(Identification of finite linear groups of permutations) on 28 July 1934.
- These groups are called Zassenhaus groups today.
- In his dissertation Zassenhaus classified all 3-fold transitive Zassenhaus groups.
- From 1934 to 1936 Zassenhaus worked at the University of Rostock and wrote his famous group theory text Lehrbuch der Gruppentheorie Ⓣ(Textbook on group theory) (1937) based on Artin's lectures at Hamburg.
- Herr Zassenhaus has rendered a most valuable service to all who are interested in this subject, and we shall await the publication of the later volumes with impatience.
- Zassenhaus became Artin's assistant at Hamburg in 1936.
- Zassenhaus found that a normal academic career was made impossible for him because of his intense dislike of the Nazi party.
- This in fact happened in 1942, when somehow Tietz's presence as a secret student at the university became known and a denunciation was threatened: Zassenhaus warned Tietz, and Hecke immediately cancelled the class, giving back the student fees.
- In fact, Tietz only discovered much later that Zassenhaus was connected with a resistance effort that helped hide endangered people.
- The teaching Zassenhaus did at Hamburg University after 1940 was unofficial, he had to join the Nazi party if he was to keep his position and Zassenhaus was not prepared to do this.
- Zassenhaus worked on a broad range of topics and, in addition to those mentioned above, he worked on nearfields, the theory of orders, representation theory, the geometry of numbers and the history of mathematics.
- Professor Zassenhaus took a profound interest in teaching of mathematics at all levels.
- In 1982, Zassenhaus retired but continued to be associated with Ohio State University.
- Zassenhaus, who was a member of the First English Lutheran Church in Columbus, died in the Hospice of Columbus.

Born 28 May 1912, Koblenz-Moselweiss, Germany. Died 21 November 1991, Columbus, Ohio, USA.

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Algebra, Group Theory, Origin Germany

**O’Connor, John J; Robertson, Edmund F**: MacTutor History of Mathematics Archive