Her research is concentrated on number theory and combinatorics, with connections to a number of other areas, including analysis, dynamical systems, and physics. She initiated new subareas and discovered unexpected connections between disparate fields. She was one of the closest collaborators of Paul Erdős with 35 joint papers, and she mentored generations of Hungarian combinatorists. Her active research career spanned more than six decades. One of her foundational papers in the emerging area of graph limits, with Borgs, Chayes, Lovász, and Vesztergombi, appeared in the Annals of Mathematics in 2012, at her age of 82.
She was elected to the Hungarian Academy of Sciences (1985), the Austrian Academy of Sciences (1995), and the Academia Europaea (2013), and received a number of prestigious awards. She was awarded an Honorary Doctorate by Eötvös University, Budapest, her alma mater, in 2014, and by the Hebrew University, Jerusalem in 2018.
Her passing marks the end of an era that has seen dramatic growth in combinatorics both in the volume of knowledge and the depth of the field’s interaction with and influence on mathematics in general, a growth to which Sós has significantly contributed.
It was an era marked by names like Paul Erdős, Paul Turán, Tibor Gallai, and Alfréd Rényi, towering figures on the combinatorics scene from the late 1930s (and working in a number of other areas, including number theory, analysis, probability). They were Sós’s mentors, close personal friends and collaborators. They, like Sós herself, were also Holocaust survivors (except for Erdős who spent the Nazi period of Hungary in the safety of the United States). Sós married Turán in 1952 and they had two children.
From the mid 1960s, Sós’s roles as a researcher, mentor, organizer of a string of highly successful international meetings, her participation in all aspects of the mathematical public life in Hungary, and her unfailing attention to the lives and careers of generations of her colleagues made her perhaps the central figure of the Hungarian combinatorics community, a group that has, over the decades, produced many of the new directions and breakthroughs that shaped the development of combinatorics globally. The famed weekly Hajnal–T. Sós seminar she ran for over four decades together with András Hajnal, another mentee and prolific collaborator of Erdős, was the forum where seminal results like Szemerédi’s Theorem on arithmetic progressions, Lovász’s and Bárány’s proofs of Kneser’s Conjecture, Ajtai’s results on bounded-depth Boolean circuits, Beck’s work in discrepancy theory, and many more, now classical, results were first presented.
In 1983, the Communist government of Hungary, cautiously breaking from Moscow’s rigid doctrine, allowed teaching enterprises to be formed, with considerable degree of freedom to use the proceeds from tuition. This meant that the best instructors could be hired, and paid at competitive rates. Sós and László Lovász were the first to realize the potential of the new rule. They contacted me (I was spending a semester at the University of Oregon at the time), and the idea of BSM was born. While I was working on marketing the program in the US and Canada, Sós and Lovász neutralized the bureaucratic obstacles in Budapest, and found the right allies who would then create the infrastructure of the program there. Sós was fond of the program and remained its steadfast supporter all her life. Her graceful presence at each of the BSM reunions in Budapest and the warmth with which she greeted former and current program officers and alumni added to the sense of community at those events.
Sós’s leadership, her tireless work on behalf of the community she was instrumental in building, her warm personal attention to many of us across generations will be dearly missed.
April 9, 2023
University of Chicago
(C) 2023 Laszlo Babai
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