Helmut Ulm

His Habilitationsschrift developed a generalization of the elementary divisor theory to infinite matrices, continuing ideas of Ulm's teacher Toeplitz.

It was submitted in Münster in 1936 and refereed by Heinrich Behnke, Gottfried Köthe, F. K. Schmidt, and B. L. van der Waerden.

Besides his three important papers on the classification of infinite abelian groups, Ulm published only a few notes in the proceedings of the Münster mathematical seminar, one of which dealt with solution of systems of linear equations by a computer.

During the World War II, Ulm worked as a cryptographer at Pers Z S starting in August 1941 on a part-time basis from Thursday through to Saturday and on Monday through Wednesday at Münster.

[1] After the war he mostly taught courses in applied mathematics and supervised several Ph.D. theses; those of G. Tillmann (1952) and G. Roth (1961) were close to his old work on infinite-dimensional linear algebra and infinite groups.