FROM THE AMS SECRETARY

2019 Leroy P. Steele Prizes

The 2019 Leroy P. Steele Prizes were presented at the 125th Annual Meeting of the AMS in Baltimore, Maryland, in January 2019. The Steele Prizes were awarded to Haruzo Hida for Seminal Contribution to Research, to Philippe Flajolet and Robert Sedgewick for Mathematical Exposition, and to Jeff Cheeger for Lifetime Achievement.

Haruzo Hida Philippe Flajolet Robert Sedgewick Jeff Cheeger

Citation for Seminal Contribution to Research: Hamadera (presently, Sakai West-ward), Japan, he received Haruzo Hida an MA (1977) and Doctor of Science (1980) from Kyoto The 2019 Leroy P. Steele Prize for Seminal Contribution to University. He did not have a thesis advisor. He held po- Research is awarded to Haruzo Hida of the University of sitions at Hokkaido University (Japan) from 1977–1987 California, Los Angeles, for his highly original paper “Ga- up to an associate professorship. He visited the Institute for Advanced Study for two years (1979–1981), though he lois representations into GL2(Zp[[X ]]) attached to ordinary cusp forms,” published in 1986 in Inventiones Mathematicae. did not have a doctoral degree in the first year there, and In this paper, Hida made the fundamental discovery the Institut des Hautes Études Scientifiques and Université that ordinary cusp forms occur in p-adic analytic families. de Paris Sud from 1984–1986. Since 1987, he has held a J.-P. Serre had observed this for Eisenstein series, but there full professorship at UCLA (and was promoted to Distin- the situation is completely explicit. The methods and per- guished Professor in 1998). spectives that Hida introduced have been used in the past Hida’s main research interests lie in arithmetic geometry, three decades to solve fundamental problems in the theory both Archimedean and Henselian, through the automor- of p-adic Galois representations and p-adic L-functions, and phic approach (initiated by Erich Hecke). He was an invited they have led to progress on p-adic analogues of the conjec- speaker at the ICM in Berkeley (1986), a Guggenheim fel- ture of Birch and Swinnerton-Dyer. Hida families are now low (1991–1992), a recipient of the Spring Prize from the ubiquitous in the arithmetic theory of automorphic forms, Mathematical Society of Japan (1992), a senior scholar at and his research has changed the way we view the subject. the Clay Mathematics Institute (2010–2011), an inaugural fellow of the American Mathematical Society (2012), and a Biographical Note: Haruzo Hida recipient of a Docteur Honoris Causa, Universitée de Paris Haruzo Hida is a Distinguished Professor of mathe- XIII (2015). He is the author of seven research books and matics at UCLA. Born in 1952 in the beach resort town of monographs on his own results.

594 Notices of the American Mathematical Society Volume 66, Number 4 FROM THE AMS SECRETARY

Response from Haruzo Hida Citation for Mathematical Exposition: It is a great honor (and also a big surprise) to receive Philippe Flajolet and Robert Sedgewick the Leroy P. Steele Prize for Seminal Contribution to Re- The 2019 Leroy P. Steele Prize for Mathematical Exposi- search from the AMS. Why a surprise? The name of the tion is awarded to Philippe Flajolet (posthumously) of town Hamadera appears (as “Takashi-no-Hama”) in the the Institut National de Recherche en Informatique et en sixth–eighth-century Japanese “Tan-ka/Chou-ka” poem Automatique (INRIA) and Robert Sedgewick of Princeton anthology “Manyou-shu” (Ten thousand leaves), and by a University for their book Analytic Combinatorics (Cam- tradition of the town, I was familiar with the ancient poems bridge University Press, Cambridge, 2009), an authoritative at an early age (as they are all written in Japanese pho- and highly accessible compendium of its subject, which netic symbols, so, easy to read). Starting with the poems, demonstrates the deep interface between combinatorial I enjoyed Japanese and Chinese classics. Chinese poems mathematics and classical analysis. It is a rare work, one by a decadent Japanese Zen monk of the fifteenth century that defines the relatively young subject in its title, mixing greatly impressed me; they could be interpreted (with a equal parts of complex analysis and combinatorial struc- question mark) to suggest the purpose of one’s life could ture. The authors have combined their extraordinary ana- be found only in an enjoyable pastime (or more precisely, lytical and expository skills to organize the entire subject a way to kill time), lasting until one’s demise. From that into a well-developed and fascinating story. Its publication time on, I tried in earnest to find such a way to kill time. I in 2009 was a major event, and as a result, analytic combi- finally found one accidentally in the mid-1970s and, after natorics is now a thriving subdiscipline of combinatorial that, became totally addicted to math. Therefore, I am and stochastic mathematics, as well as a key component of hardly professional nor academic in mathematical work, the analysis of algorithms. and I often create mathematics without tangible reference Quoting Robin Pemantle’s 2010 review of Analytic Com- to contemporaries. It seems unfair that such a person would binatorics, published in SIAM Review, “This is one of those be chosen for a prestigious AMS prize. Nevertheless, my books that marks the emergence of a subfield.” The book work has found some deep applications. This hopefully magically summarizes a vast amount of information. It legitimizes the award. identifies and expounds key techniques that have never A seventeenth-century Japanese playwright told a Con- been explained so well before, while consistently paying fucianist that creating a play is to walk the boundary of proper attention to the historical context. It features world- imaginary and real (or dream and truth) without stepping class graphics and typesetting and a definitive bibliography. out of the narrow path. When in 1975 I started to study The book is largely self-contained and a pleasure to read— (with Koji Doi) the relation between congruence and any mathematician can use it as the basis for teaching a L-values, Doi told me that a Hecke eigenform appears course on analytic combinatorics as an undergraduate to have siblings having eigenvalues (of Hecke operators) elective in mathematics. congruent modulo a (parent) prime with the eigenval- ues of the initial form. While at IAS, I felt that pathwise Biographical Note: Philippe Flajolet connectedness of the Archimedean topology forces the Philippe Flajolet (1948–2011) was an extraordinary French core cuspidal spectrum of Hecke operators to be discrete; mathematician and computer scientist. He graduated from so, under a Henselian topology, totally disconnected, I École Polytechnique in Paris in 1970, obtained a PhD imagined that the spectrum is prevalently continuous. from Université Paris 7 with Maurice Nivat in 1973 and a After having returned to Japan in the fall of 1981, I started Doctorate in Sciences from the University of Paris at Orsay making progress in proving this guess and succeeded (par- in 1979. He spent his career at INRIA in Rocquencourt, tially) in getting a proof via arithmetic geometry by the France, where he eventually led the ALGO research group, end of January 1982. Since the result seemed too strong, which produced numerous outstanding young scientists I sought one more proof. I got another via Betti Étale co- and attracted visiting researchers from all over the world. homology of modular curves within a couple of months. He held numerous visiting positions: at Waterloo, Stan- Afterwards, I sent out preprints to senior number theorists ford, Princeton, Wien, Barcelona, IBM, and Bell Laborato- I’d encountered at Princeton. The second proof is in the ries. He received several prizes, including the Grand Science paper published in 1986 for the award (and now there are Prize of UAP (1986), the Computer Science Prize of the more than two proofs). French Academy of Sciences (1994), and the Silver Medal Since I enjoy finding results independent of my fellow of CNRS (2004). He was elected a Corresponding Member mathematicians, I did not make too much effort to find (Junior Fellow) of the French Academy of Sciences in 1994, applications to classical questions posed by others, but a a Member of the Academia Europaea in 1995, and a Mem- handful of excellent number theorists became interested ber (Fellow) of the French Academy of Sciences in 2003. in later years, and found good applications for my result. He was made a knight of the Légion d’Honneur in 2010.

April 2019 Notices of the American Mathematical Society 595 FROM THE AMS SECRETARY

Flajolet’s extensive and far-reaching research in mathe- massive open online courses (MOOCs) and published matics and computer science spanned formal languages, extensive online content on analysis of algorithms and ana- computer algebra, combinatorics, number theory, and anal- lytic combinatorics and, with Kevin Wayne, algorithms and ysis, all oriented toward the study of algorithms and discrete computer science. These materials have made it possible structures. During his forty years of research, he contributed and convenient for millions of people around the world to nearly 200 publications. An important proportion of these teach and learn these subjects, particularly in regions where are foundational contributions or represent uncommon access to higher education is difficult. breadth and depth. Highlights range from pioneering work in computer algebra in the 1980s to theorems in asymptotic Response from Robert Sedgewick analysis in the 1990s that inspired decades of later research This award is thrilling and humbling for me, but also bit- to a probabilistic algorithm that is widely used in modern tersweet, because Philippe is not here to share it. But all cloud computing. Much of his research laid the foundation of us who were there vividly remember his excitement at for the development, with Sedgewick, of the subfield of our event in Paris on the occasion of his sixtieth birthday mathematics that is now known as analytic combinatorics, when we presented him with the first printed copy of a calculus for the study of discrete structures. Analytic Combinatorics. I keep the look on his face at that These research contributions will have impact for gen- moment fresh in my mind and know that the same look erations. Flajolet’s approach to research, based on endless would grace us now. curiosity, discriminating taste, deep knowledge, relentless Philippe and I (and many others) were students of the computational experimentation, broad interest, intellectual work of Don Knuth in the 1970s, and inspired by the idea integrity, and genuine camaraderie, will serve as an inspira- that it was possible to develop precise information about tion for years to come to those who knew him. the performance of computer programs through classical analysis. When we first began working together in 1980, Biographical Note: Robert Sedgewick our goal was just to organize models and methods that we Robert Sedgewick is the William O. Baker Professor in the could use to teach our students what they needed to know. Department of Computer Science at Princeton University. As we traveled between Paris and Princeton, producing Born in 1946 in Willimantic, Connecticut, he graduated conference papers, journal articles, and INRIA research from Brown University in 1968 and did his doctoral work reports, we began to understand that something more with Donald E. Knuth at Stanford University, receiving his general was at work, and Analytic Combinatorics began to PhD in 1975. After ten years on the faculty at Brown, he emerge. It is particularly gratifying to see citations of the left to be the founding chair of Princeton’s Department of book by researchers in physics, chemistry, genomics, and Computer Science in 1985. He served for twenty-six years many other fields of science, not just mathematicians and as a member of the board of directors of Adobe Systems computer scientists. and has held visiting research positions at Xerox PARC, Analyzing algorithms is challenging—at the outset, IDA, INRIA, and Bell Laboratories. known results were often either excessively detailed or Sedgewick is the author of twenty books. He is best rough, questionably useful approximations. Thus, what fun known for Algorithms, which has been a best-selling text- it was to consider the idea that maybe (despite the formi- book since the early 1980s and is now in its fourth edition. dable barrier of the Halting Problem) one could develop His other current textbooks include An Introduction to the a black box that could take a program as input and pro- Analysis of Algorithms and Analytic Combinatorics (with duce as output an asymptotic estimate of its running time. Philippe Flajolet) and Computer Science: An Interdisciplinary How challenging it was to develop a rigorous calculus that Approach (with Kevin Wayne). takes us from simple formal descriptions of combinatorial Beyond his work with Flajolet on analytic combina- objects through properties of generating functions in the torics, Sedgewick’s research is characterized by a scientific complex plane to precise information about the objects. approach to the study of algorithms and data structures, How exciting it was to build on this work to develop theo- where careful implementations and appropriate mathe- rems of sweeping generality that encompass whole families matical models are validated by experimentation and then of combinatorial classes. As Philippe said, developing new used to understand performance and develop improved theorems like these “constitutes the very essence of analytic versions. Many of his research results are expressed in his combinatorics.” Algorithms books, and his implementations routinely serve With a vibrant community of researchers working on as reference and are featured throughout our global com- developing and applying such theorems, I suspect and hope putational infrastructure. that the story of analytic combinatorics is just in its infancy. In recent years, Sedgewick has been a pioneer in devel- I am particularly heartened by the statement in the oping modern approaches to disseminating knowledge, citation that any mathematician could use our book to from introductory to graduate level. He has developed six teach an undergraduate course on the subject. Having the

596 Notices of the American Mathematical Society Volume 66, Number 4 FROM THE AMS SECRETARY broadest possible reach was indeed our hope when, with Biographical Note: Jeff Cheeger the support of our editor, we provided free access to the Jeff Cheeger was born in Brooklyn, New York, in 1943. He book on the web. For the past several years, I have been graduated from Erasmus Hall High School in 1960 and working hard to apply twenty-first-century tools to develop from Harvard College in 1964. He received his PhD from a unique resource for teaching this material. Anyone can Princeton under Salomon Bochner and James Simons in now teach and learn Analytic Combinatorics using the stu- 1967. After a year in Berkeley as an NSF Postdoctoral Fel- dio-produced lecture videos, new problems with solutions, low and a year at the University of Michigan as an assistant ac.cs.princeton. and other online content found at professor, he moved to Stony Brook, where he remained for edu . Philippe, who always embraced technology, would be the next twenty years, rising to the rank of Distinguished particularly pleased with the idea that it now makes ana- Professor. Since 1989, he has been a member of the Cou- lytic combinatorics accessible to large numbers of people rant Institute, where since 2003 he has been Silver Professor around the world. of Mathematics. Citation for Lifetime Achievement: Jeff Cheeger Cheeger has given invited addresses at the International The 2019 Leroy P. Steele Prize for Lifetime Achievement is Congress of Mathematicians in 1974 and 1986. He was awarded to Jeff Cheeger of the Courant Institute, New York awarded the Max Planck Research Prize of the Alexander University, for his fundamental contributions to geometric von Humboldt Society in 1996 and the Oswald Veblen analysis and their far-reaching influence on related areas Prize of the AMS in 2001. He was elected to the National of mathematics. For more than half a century, Jeff Cheeger Academy of Sciences in 1997, the Finnish Academy of has been a central figure in differential geometry and, more Science and Letters in 1998, and the American Academy broadly, geometric analysis. His work on the profound and of Arts and Sciences in 2006. He was elected a Fellow of subtle effects of curvature on the topology and geometry the AMS in 2012. of manifolds, often under very weak regularity conditions, Response from Jeff Cheeger has laid and continues to lay foundations for much of the progress in these areas ever since his 1967 dissertation. It is a great honor to have been awarded the Leroy P. Steele His work, both alone and in collaboration with others, Prize for Lifetime Achievement. It is especially gratifying to has yielded such spectacular results as the Soul and Splitting have received an award for research done over my whole Theorems (with Detlef Gromoll) and the Compactness career and for which the citation includes work with a and Collapsing Theories (with Kenji Fukaya and Misha number of remarkable mathematicians, the interactions Gromov), which have been among the most important with whom have enriched my life. I would particularly like developments in geometry in the past three decades. These to thank my collaborators Paul Baum, Detlef Gromoll, Jim fundamental theories have had far-reaching consequences, Simons, S.-T. Yau, Michael Taylor, Werner Muller, Robert for instance, playing an essential role in Perelman’s res- Schrader, Misha Gromov, Jean-Michel Bismut, Mike Ander- olution of the Poincaré conjecture. Cheeger’s inequality son, Gang Tian, Xiaochun Rong, Xianzhe Dai, Kenji Fukaya, bounding from below the first nonzero eigenvalue of the Toby Colding, Bruce Kleiner, Assaf Naor, and Aaron Naber. Laplacian in terms of a certain isoperimetric constant, I would also like to acknowlege the influence of my friends known as Cheeger’s constant, has had numerous applica- Blaine Lawson, Dennis Sullivan, and Is Singer. tions, as has his work on the Hodge theory and spectral I was introduced to mathematics by my father, Thomas geometry of singular spaces, the structure theory of spaces Cheeger, a structural engineer. He could not have given with bounds on Ricci curvature, his resolution of the Ray– me a better gift. My mother, Pauline, stressed to me the Singer Conjecture, the theory of differential characters (with benefits of hard work. James Simons), his work on differentiability of Lipschitz In junior high school, I made a very good friend, Mel functions on metric measure spaces, and many others have Hochster, with whom I could share my interest in mathe- been the fundamental tools that enabled major advances matics. It was exciting and fun. When I was an undergrad- in geometry and analysis that continue to bear fruit and uate at Harvard, two professors, Shlomo Sternberg and shape the field. Raoul Bott, made a big impression. They introduced me to differential geometry and algebraic topology. Beyond that, they conveyed the feeling that being a mathematician was something like being a member of a special order, an order into which one could hope to one day be initiated. During my last year, I took a PDE course from Jim Simons. In graduate school at Princeton, along with my official ad- visor, Salomon Bochner, Jim became my teacher and then my friend. I owe him a lot.

April 2019 Notices of the American Mathematical Society 597 FROM THE AMS SECRETARY

I was very lucky to have found my way into differential About the Prizes geometry which, I have come to believe, was the right area The Leroy P. Steele Prizes were established in 1970 in for my particular turn of mind. When I started, it was a bit honor of George David Birkhoff, William Fogg Osgood, out of fashion, underdeveloped, not overly competitive, but and William Caspar Graustein. Osgood was president of poised to take off. For me, this was ideal. Later, I learned the AMS during 1905–1906, and Birkhoff served in that some analysis, which opened up new vistas. capacity during 1925–1926. The prizes are endowed under As reseachers, our job is to produce new mathematics. the terms of a bequest from Leroy P. Steele. Up to three Still, looking back over a whole career, it is somewhat mind prizes are awarded each year in the following categories: blowing to realize how little we understood when I began, (1) Lifetime Achievement: for the cumulative influence of as compared to what has since been discovered. the total mathematical work of the recipient, high level of research over a period of time, particular influence on From the time I was young, I was struck by the fact that in the development of a field, and influence on mathematics mathematics, questions have a right or wrong answer. This through PhD students; (2) Mathematical Exposition: for a has a consequence. With small exceptions, mathematicians book or substantial survey or expository research paper; (3) tend to genuinely admire each other’s achievements. An- Seminal Contribution to Research: for a paper, whether re- other thing, as mathematicians we have quite direct access cent or not, that has proved to be of fundamental or lasting to some of the most original minds of the past and of the importance in its field or a model of important research. present. From such people, if you keep your ears open, you The Prize for Seminal Contribution to Research is awarded can really learn something. Finally, we are lucky in that on a six-year cycle of subject areas. The 2019 prize was we get to think about what we want and to interact with open; the 2020 prize will be given in analysis/probability; brilliant young people. I feel very fortunate to have had a the 2021 prize in algebra/number theory; the 2022 prize in life in mathematics. applied mathematics; the 2023 prize in geometry/topology; and the 2024 prize in discrete mathematics/logic. The Leroy P. Steele Prizes for Mathematical Exposition and Seminal Contribution to Research carry a cash award of US$5,000; the Prize for Lifetime Achievement, a cash award of US$10,000. The Steele Prizes are awarded by the AMS Council act- ing on the recommendation of a selection committee. The members of the committee for the 2019 Steele Prizes were: •• Robert L. Bryant, •• Tobias H. Colding, •• Eric M. Friedlander, •• Mark L. Green, •• B. H. Gross (Chair), •• Carlos E. Kenig, •• Dusa McDuff, •• Victor Reiner, •• Thomas Warren Scanlon

The list of previous recipients of the Leroy P. Steele Prizes may be found on the AMS website at https://www.ams .org/profession/prizes-awards/ams-prizes /steele-prize.

Credits Photos of the winners were provided by each of them.

598 Notices of the American Mathematical Society Volume 66, Number 4