András Hajnal was a mathematician working in set theory and combinatorics. He served as director of DIMACS and later as a Rutgers mathematics professor before returning to Hungary after retirement.[ref]
https://www.math.rutgers.edu/people/department-directory/detail/343-in-memoriam/2066-hajnal-andras. Institutional memorial, 1931–2016 and career
One result bearing his name, proved with Paul Erdős, says that every infinite set admits an omega-Jónsson function: a colouring of its countably infinite subsets by its elements such that every subset of the same cardinality still sees every colour. Assuming the axiom of choice, even restricting to a large subset cannot simplify this colouring by omitting a colour. This illustrates the negative side of infinite partition relations, complementing Ramsey theory results that force homogeneous subsets.[ref]
András Hajnal, Rutgers memorial portrait
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András Hajnal is a prominent Hungarian mathematician known for his contributions to set theory, combinatorics, and mathematical logic. He is particularly recognized for his work in graph theory and for Hajnal's theorem, which deals with properties of graphs and their colorings. Hajnal's research has significantly impacted these fields, and he is often cited in academic papers related to combinatorial set theory.