The synchronization course is over. After eight hours of lectures between lunchtime yesterday and lunchtime today, I am quite tired. Did it go well? You have to ask the students that; but for me it went well, since there were many good questions from the audience.

I was delighted to see Dima Pasechnik in the audience. You may remember from the last posting about synchronization that Dima helped me greatly with proofreading the notes, and that his student Nick Gravin solved one of my open problems.

But this morning Dima brought sad news: the death yesterday of Dima Fon-Der-Flaass from cancer.

Dima (Fon-Der-Flaass) was a postdoc here in the early 1990s. At that time, Michel Deza described him as my son, since like me he was a mathematician of very wide interests. Also, unlike me, he was very quick on his feet mathematically. We wrote two papers together, one about a certain permutation of the set of antichains in a poset (a follow-up of a paper which had originally brought Dima to my attention), and one on permutation groups whose bases satisfy the matroid bases axioms. In addition, we wrote a set of Fibonacci notes based on talks we gave in the Combinatorics Study Group, which have been quite influential in their way; I think DIma was pleased with his part.

It is not just coincidence that this news comes in a post that began on the subject of synchronization. This is a subject with such a wide range of connections that it was really up Dima’s street. In fact, he made a posting to his own site drawing people’s attention to mine.

There is, I believe, a Zen saying, a wish for prosperity: “Father die, son die, grandson die”. The point of this paradoxical statement is that this is the proper order; if the son dies before the father, or the grandson before either, a huge gap is left. Well, Dima has gone before me, and I miss him.