I was very saddened to read on T. Tao’s blog of the death of Elias Stein. Although I did not know him personally, or even worked in the same area of mathematics, I felt a great admiration and respect for him. I remember browsing intently through some of his books, especially at the beginning of my PhD thesis, but also still in recent times, and especially the one (partly) about quasi-orthogonality. I tried to apply one of the statements I found there (“Cotlar’s Lemma”) to some cases of large-sieve inequalities. It didn’t work, but I remember that during a party at Fine Hall some time later, my advisor H. Iwaniec introduced me to Stein (this was my only personal encounter with him!) by saying jokingly that “Your lemma is not strong enough”.
I have always felt a great attraction to the type of harmonic analysis that I read about in those books, even if I don’t understand it. Maybe, one day, I will be able to know more…