**András Hajnal** was a Hungarian mathematician who worked on set theory, particularly combinatorial set theory, set theoretic topology and combinatorics. He wrote over 60 joint papers with Erdős.

- During the years 1941-42 the two schools had merged and when Hajnal began his studies there it was a single school named the Berzsenyi Dániel Gimnázium but operating in the buildings of the former Bolyai school.
- Although the school had a good reputation for mathematics and science, most of Hajnal's contemporaries and friends at the school were oriented towards the humanities.
- While at the Gimnázium, Hajnal was not particularly interested in mathematics.
- An important factor in Hajnal's school days was his involvement with the Vörösmarty scout troop.
- Many of Hajnal's school friends were also in the Vörösmarty scout troop, including István Eörsi, and it provided an important influence on the young boy, although not towards mathematics for again the members were more oriented to the humanities or the law.
- Given what we have just recorded about Hajnal's school abilities and the influences on him, there is an obvious question.
- Hajnal, however, was doing mathematics out of choice.
- When Szász singled him out as one of the best two students in the class, Hajnal began to realise that he had some abilities.
- It was Rózsa Péter who taught a set theory course but Hajnal felt he did not understand it so he read a book on set theory, in fact in was the first mathematics book that he read.
- Rózsa Péter was an excellent teacher, so Hajnal's friends thought that he was saying he did not understand her lectures just to annoy her.
- In 1953 Hajnal graduated from Eötvös Loránd University with a degree which allowed him to teach in secondary schools.
- In 1956 Hajnal was awarded the degree of Candidate of Mathematical Sciences (equivalent to a Ph.D.) for his dissertation On a consistency theorem connected with the generalized continuum problem.
- Just before he submitted his dissertation, Hajnal had met Pál Erdős in the summer of 1956.
- Erdős and Hajnal provided the context, spurred the possibilities, and got enticingly close to a transformative result.
- This was the first of over 60 joint papers by Hajnal and Erdős.
- On 1 September 1956 Hajnal went to Budapest to take up a faculty position at Eötvös Loránd University.
- They had one son, Peter Hajnal who studied mathematics but became a philosopher.
- Peter Hajnal became the co-dean of the European College of Liberal Arts.
- András and Emilia Hajal went to the United States on a number of occasions, the first being for a year in Berkeley in 1963.
- This did not suit Hajnal at all so he became a professor at Rutgers University where he could teach students.
- Perhaps the best known of these is the Hajnal-Szemerédi theorem on equitable colouring of graphs that proved a conjecture of Erdős.
- One of Hajnal's loves outside mathematics was playing chess.
- In October 1999 a Hajnal Conference was held at DIMACS.
- In order to provide András with a pleasant weekend in the midst of his treatment, it was decided that an international conference on Set Theory should be organised in his honour.
- As the scheduled date of the conference drew nearer, there was some concern that it might coincide with András's surgery.
- A week before, it finally became clear that András's treatment had been successful and the conference turned into a celebration of his complete recovery.
- Because of the respect and deep affection which everybody in Set Theory has for András, there was no difficulty in putting together an outstanding program, which included many of the leaders in the field.
- Of course, there could be no question that András fully deserved a conference in his honour.
- However, especially before it became clear that he would fully recover his health, it seemed a little indelicate to officially refer to it as the Hajnal Conference.
- (Somebody made the slightly bizarre suggestion that it should be advertised as a conference to celebrate András's 68th birthday.) But now two years have passed and we can finally openly admit that the conference was held in honour of András and dedicate these Proceedings to him on the occasion of his 70th birthday.
- A Colloquium honouring the 70th birthdays of both Hajnal and Vera Sós was organised by the János Bolyai Mathematical Society and the Mathematical Institute of the Hungarian Academy of Sciences in January 2001 in Budapest; it was on 'Finite and Infinite Combinatorics'.
- The Alfréd Rényi Institute of Mathematics, The János Bolyai Mathematical Society and the Mathematical Institute of Eötvös University organised the conference 'Set Theory and Combinatorics' in the Alfréd Rényi Institute, Budapest to celebrate Hajnal's 80th birthday in June 2011.
- Hajnal was honoured by being elected a fellow of the American Mathematical Society in 2012.

Born 13 May 1931, Budapest, Hungary. Died 30 July 2016, Budapest, Hungary.

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Origin Hungary

**O’Connor, John J; Robertson, Edmund F**: MacTutor History of Mathematics Archive