Ákos Császár ( hu, Császár Ákos, ) (26 February 1924,

Budapest Budapest (, ; ) is the capital and most populous city of Hungary. It is the ninth-largest city in the European Union by population within city limits and the second-largest city on the Danube river; the city has an estimated population ...

– 14 December 2017, Budapest) was a Hungarian

mathematician A mathematician is someone who uses an extensive knowledge of mathematics in their work, typically to solve mathematical problems. Mathematicians are concerned with numbers, data, quantity, structure, space, models, and change. History On ...

, specializing in

general topology In mathematics, general topology is the branch of topology that deals with the basic set-theoretic definitions and constructions used in topology. It is the foundation of most other branches of topology, including differential topology, geomet ...

and

real analysis In mathematics, the branch of real analysis studies the behavior of real numbers, sequences and series of real numbers, and real functions. Some particular properties of real-valued sequences and functions that real analysis studies include converg ...

. He discovered the

Császár polyhedron In geometry, the Császár polyhedron () is a nonconvex toroidal polyhedron with 14 triangular faces. This polyhedron has no diagonals; every pair of vertices is connected by an edge. The seven vertices and 21 edges of the Császár polyhedron ...

, a nonconvex

polyhedron In geometry, a polyhedron (plural polyhedra or polyhedrons; ) is a three-dimensional shape with flat polygonal faces, straight edges and sharp corners or vertices. A convex polyhedron is the convex hull of finitely many points, not all on th ...

without diagonals. He introduced the notion of syntopogeneous spaces, a generalization of

topological space In mathematics, a topological space is, roughly speaking, a geometrical space in which closeness is defined but cannot necessarily be measured by a numeric distance. More specifically, a topological space is a set whose elements are called points ...

s. During the end of 1944 his grandfather lost his life during the siege of Budapest. Then his father, older brother and himself were arrested by the Germans and sent to a concentration camp approximatively 45 miles east of Budapest. An infectious illness spread in the camp, and his brother and father died, but Ákos survived. He is a member of the group of five students of the late professor

Lipót Fejér Lipót Fejér (or Leopold Fejér, ; 9 February 1880 – 15 October 1959) was a Hungarian mathematician of Jewish heritage. Fejér was born Leopold Weisz, and changed to the Hungarian name Fejér around 1900. Biography Fejér studied mathematic ...

who called them "The Big Five". The other four are John Horvath, János Aczél,

Steven Gaal Steven Alexander Gaal (February 22, 1924 – March 17, 2016) (also known as István Sándor Gál or I. S. Gál) was a Hungarian- American mathematician and Professor of Mathematics at the University of Minnesota—Minneapolis. Education Ga ...

and

László Fuchs László Fuchs (born June 24, 1924) is a Hungarian-born American mathematician, the Evelyn and John G. Phillips Distinguished Professor Emeritus in Mathematics at Tulane University.

, all of whom are now retired mathematics professors in North America.Tribute to the achievements of five outstanding Hungarian mathematicians
Department of Mathematical Sciences of the Hungarian Academy of Sciences Only Császár became a university professor in Budapest. Between 1952 and 1992 he was head of the Department of Analysis at the

Eötvös Loránd University Eötvös Loránd University ( hu, Eötvös Loránd Tudományegyetem, ELTE) is a Hungarian public research university based in Budapest. Founded in 1635, ELTE is one of the largest and most prestigious public higher education institutions in Hung ...

, Budapest. Corresponding member (1970), member (1979) of the

Hungarian Academy of Sciences The Hungarian Academy of Sciences ( hu, Magyar Tudományos Akadémia, MTA) is the most important and prestigious learned society of Hungary. Its seat is at the bank of the Danube in Budapest, between Széchenyi rakpart and Akadémia utca. Its ma ...

. He has been general secretary (1966–1980), president (1980–1990), honorary president (since 1990) of the

János Bolyai Mathematical Society The János Bolyai Mathematical Society (Bolyai János Matematikai Társulat, BJMT) is the Hungarian mathematical society, named after János Bolyai, a 19th-century Hungarian mathematician, a co-discoverer of non-Euclidean geometry. It is the profes ...

. He received the

Kossuth Prize The Kossuth Prize ( hu, Kossuth-díj) is a state-sponsored award in Hungary, named after the Hungarian politician and revolutionist Lajos Kossuth. The Prize was established in 1948 (on occasion of the centenary of the March 15th revolution, the ...

(1963) and the Gold Medal of the Hungarian Academy of Sciences (2009). Császár died on 14 December 2017, aged 93.

Selected publications

* Á. Császár: A polyhedron without diagonals, '' Acta Sci. Math. Szeged'', 13(1949), 140–142. * Á. Császár: ''Foundations of general topology'', A Pergamon Press Book The Macmillan Co., New York 1963 xix+380 pp., translated from ''Fondements de la topology générale'', Akadémiai Kiadó, Budapest (1960) 231 pp. * Á. Császár: ''General topology'', Translated from the Hungarian by Klára Császár. Adam Hilger Ltd., Bristol, 1978. 488 pp.

References

1924 births 2017 deaths Topologists 20th-century Hungarian mathematicians 21st-century Hungarian mathematicians Members of the Hungarian Academy of Sciences Scientists from Budapest {{Europe-mathematician-stub