I was released as a prisoner of war on July 1, 1945, still 17 years old, and was lucky enough to be able to begin my study of mathematics, mathematical logic, and physics at the University of Münster already in the winter semester 1945/46. The University and the town were terribly destroyed, but the University began to operate. My teachers were Heinrich Behnke and Heinrich Scholz, later Karl Stein and Friedrich Karl Schmidt joined the faculty.
In 1948 I participated in a Swiss program for German students (three weeks of hard work on a farm, followed by one week to be spent freely in Switzerland). Upon recommendation of Behnke I was invited by Heinz and Anja Hopf to stay with them in their house in Zollikon near Zurich for this fourth week. I learnt a lot from Heinz Hopf about algebraic topology and complex manifolds and returned to Münster full of new ideas which I told Heinrich Behnke and Karl Stein. I spoke in their seminars. This was already basic for my dissertation under Behnke, but much inspired by Hopf. I received a stipend for the ETH Zurich for three semesters (summer 1949 to summer 1950) and became a student of Heinz Hopf, Beno Eckmann and Paul Bernays at the ETH. For a German student who had lived through the war, Switzerland was a paradise academically and otherwise. I enjoyed the international atmosphere with visitors from many countries and the excellent courses and seminars offered. But most important were my frequent discussions with Heinz Hopf at the ETH and at his home. My dissertation developed, won a prize of the ETH and was accepted in Münster by Behnke. In July 1950 I was promoted to Dr. rer. nat. by the University of Münster. In my report I try to explain how important my study in Zurich was for my academic career and how fortunate I was that such a chance was given to me shortly after the war.
My dissertation was published in two parts in Mathematische Annalen 1951 and 1953. These are the first two papers in my Collected Papers, Springer-Verlag 1987. In my report I indicate the contents of Part II of the dissertation.