BI~LA SZOKEFALVI-NAGY I 1913-1998 We Inform You

] BI~LA SZOKEFALVI-NAGY I

1913-1998

We inform you with great sorrow that B~la Sz6kefalvi-Nagy, Editor-in-chief of the Hungarian Section of the Editorial Board of our quarterly "Analysis Mathematica" passed away on December 21, 1998, at the age of 86. He was a distinguished representative of the Hungarian mathematics and a world- wide acknowledged doyen of Operator Theory. He enriched several fields of mathematics, especially Functional Analysis, with fundamental results, contributing decisively to the development of those fields. He guarded and transferred to future generations the spirit of his teachers, Frigyes Riesz and Alfred Haar, the founders of the Szeged school of mathematics. B@la Sz6kefalvi-Nagy was born on July 29, 1913 in Kolozsv£r. His father, Gyula Sz6kefalvi-Nagy was a professor of mathematics, his mother was a secondary school teacher of mathematics and physics. B~la Sz6kefalvi- Nagy started his university studies in 1931 at the University of Szeged and received his diploma with distinction in mathematics and physics. He wrote his Ph.D. thesis on isomorphic function systems, a topic closely related to the research field of Alfr@d Haar. In the first part of his scientific career, B~la Sz6kefalvi-Nagy achieved significant results in the theory of Fourier Series, Approximation Theory, and Geometry. However, his main achievements are linked to Functional Anal- ysis, more closely, to the theory of Hilbert space operators. His first book entitled "Spektraldarstellung linearer Transformationen des Hilbertschen Raumes", by "Springer Verlag" was the first concise, summarizing work on Hilbert spaces. This slim book is the best introduction to the subject even in our days. The bulky monograph "Lemons d'analyse fonctionelle", written jointly with Frigyes Riesz and published in 1952 became a basic textbook of Functional Analysis. This monograph has been translated from the original French into English, German, Russian, Chinese, Japanese, and Hungarian, as well, and has reprinted a number of times. His celebrated dilation theorem, proved in 1953, on the existence of unitary power dilations of contractions opened new perspectives in the study of nonnormal operators. Starting with this theorem, B@la Sz6kefalvi-Nagy in collaboration with Ciprian Foia~ developed a new branch in Operator Theory. Among others, they introduced an efficient calculus operating with functions analytic and bounded in the open unit disc, succeeded in providing a Jordan model to contractions that are annihilated by a nonzero function, this model is completely analogous to the finite dimensional case, and so on. They summarized their numerous results in the monograph "Analyse harmonique des op~rateurs de l'espace de Hilbert", published in 1967 and subsequently translated into English and Russian. Nowadays, this monograph is an indispensable source in Operator Theory, and has far-reaching applications in Control Theory and in the vast field of Stochastic Processes. B~la Sz6kefalvi-Nagy published 167 scientific papers in leading mathe- matical periodicals. He was a lecturer of high level, characterized by elegant and transparent style. Generations learnt from Professor Sz6kefalvi-Nagy not only the subject itself, but experienced the pleasure of disciplined, logical thinking, as well. His textbook "Real functions and function series" (orig- inally written in Hungarian) is still the best introduction to Real Function Theory. His famous weekly seminar was also attended by a great number of foreign researchers. It was an honour and real challenge to lecture there.