by Max Karoubi
I don’t remember when I met Paul for the first time, probably at the
Institute des Hautes Études Scientifiques (IHES) which he visited
many times while collaborating with
Alain Connes.
At that time, almost
40 years ago, I formulated a conjecture predicting an isomorphism
between algebraic and topological
As is well known, the Baum–Connes conjecture (BCC) is still open,
although many interesting cases are solved. There is also a “real”
version (RBCC) of BCC where the base field is the field of real
numbers instead of complex numbers. Since Paul knew of my interest in
real topological
On another occasion, Paul was interested in applications of noncommutative geometry to classical algebraic topology. As a matter of fact, Paul’s thesis was in algebraic topology and he asked me whether my version of “noncommutative cochains” could provide a better understanding of the subject of his thesis. We still do not succeed on this project but Paul will never give up if he has the intuition of a “right” point of view!
This last project gives me the opportunity to comment about Paul’s unique personality. Paul loves mathematics with a passion he shares with his students and his collaborators. He always wants to understand deeply a subject he is working on. But this passion is not at all austere: he is playing with it, going instantly from his thoughts to his immediate surroundings. I remember once we were dining in a Paris restaurant, working and laughing at the same time. Our laughs (especially Paul’s) were so loud that our next table was puzzled by these special guys: since they wanted to know our profession, we asked them to guess (with a hint that the first letter is an M). We were very proud that they thought we were musicians. On another occasion, also in a restaurant, our next table thought that Paul was a Russian prince…
As a conclusion, when looking at Paul’s bibliography, one is impressed by the variety of subjects Paul has worked on, together with outstanding mathematicians, e.g., Raoul Bott and Alain Connes, to mention a few. His most recent work with Anne-Marie Aubert and Roger Plymen on group representations is remarkably innovative.