Let me briefly report on two birthday conferences for long-time friends and colleagues Saharon Shelah and Yuri Gurevich. Yuri fest took place in Munich and on Zoom between June 20–22 2025 and Shelah’s birthday conference will be held in Vienna on July 14–15, 2025.
For my general thoughts on celebrating colleagues’ birthdays in these tragic and dangerous times, see this post.
Saharon Shelah is among the greatest and most decorated mathematicians of our time with groundbreaking contributions in model theory, set theory, combinatorics, and other areas. Among his most famous achievements are the development of classification theory in model theory, his arithmetic cardinal theory (see this post), his proof that Whitehead’s conjecture is independent from ZFC, and his effective bounds for Van der Waerden numbers in combinatorics.
Yuri Gurevich is a renowned mathematical logician who transitioned to theoretical and practical computer science, software engineering, and later, quantum computing. One of the most natural average-case complete problems was introduced in a paper by Andreas Blass and Yuri Gurevich. (Andreas and Yuri have been long-time collaborators and friends.) Saharon and Yuri also coauthored a few important papers, including one on monadic second-order theories.
I’ve known both Saharon and Yuri since the late 1970s. Over the years, I would occasionally visit Saharon’s office (and now that I think about it, I should have taken a picture of it) to discuss interesting problems. These conversations contributed to Saharon’s generalization of Arrow’s theorem and to his work with Micha Perles on “n-convexity.” Once, Saharon asked me to comment on an introduction for the general mathematical audience to his second book on classification theory. In 1994, Saharon and I shared the Pólya Prize in Combinatorics. My daughter was a classmate of Saharon’s son, so we also met occasionally at school events.
My friendship with Yuri began at Microsoft in the late 1990s. As a complete layman, I was fascinated by his approach to software engineering, which had a major impact on Microsoft. Yuri, in turn, was interested in my views on quantum computing—well before he became an active researcher in the field in 2013—and we discussed the topic frequently over the years. We also shared an interest in detecting deception using mathematical tools (see this post by Omer Reingold on his approach).
Heartfelt congratulations to Saharon and Yuri!
Ronald de Wolf’s lecture on quantum proofs to classical theorems.
At YuriFest, Ronald de Wolf gave a great lecture on quantum proofs for classical theorems (the audio is a bit weak—turn the volume to 100%). One of his examples is discussed in this post. Yuri himself gave a wonderful talk titled The nature of nondeterministic probabilistic, quantum, etc. algorithms.
Reminder: Joram’s seminar on hypercontractivity and groups, Wednesday and Thursday, July 9 and 10, 2025.