## Professor Deane Yang, Polytechnic University, Brooklyn, NY, responds to the *New Yorker* article

### September, 2006

Subject: Original version of letter I wrote to the *New Yorker*

As a mathematician with a longstanding interest in both the Ricci flow and Poincaré conjecture, I found Nasar and Gruber's article on the Poincaré conjecture entertaining and well written. The juxtaposition of Perelman's ascetism against Yau's ambitions makes for a dramatic story. I would, however, like to say a few words in defense of Yau.

When I was growing up, I used to hear a lot of gossip from my father (who was also a mathematician) and his friends. Based on this, I used to explain to my friends how Chern was the undisputed emperor of Chinese mathematics and how various people were fighting to be Chern's successor. However, when Yau came along, it quickly became clear, from both his prodigious talents and his personality, that he would be the one. Like anyone who becomes emperor (including Chern), Yau clearly had the outsized ego and ambition required. And like many with these qualities, Yau has done things that dismay his peers. Until Perelman scooped Hamilton and Yau by proving the Poincaré conjecture, all of this stayed within the mathematical community. But Nasar and Gruber have now exposed some of this to the public.

What I don't want to be forgotten are the enormous contributions Yau has made to the mathematical community. Beyond his groundbreaking research in differential geometry, algebraic geometry, differential topology, and mathematical physics, he is one of the greatest teachers, having trained — according to the Mathematical Genealogy Project — 34 students and 124 descendants in all, including many of the top geometers working today. And he has always been generous in his support of people who are stuck in less well known institutions but doing work that impresses him (my colleagues Erwin Lutwak and Gaoyong Zhang are two examples). Yau's impact on mathematics and the mathematical community is difficult to overstate, and it is virtually all positive.

Sincerely,

Deane Yang

Professor of Mathematics

Polytechnic University