Jean-Pierre Kahane


Born: 11 December 1926 in Paris, France
Died: 21 June 2017 in Paris, France

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Jean-Pierre Kahane was the son of Ernest Kahane (1903-1996) and Marcelle Élise Jeanne Wurtz (1900-1991). The family were Jewish, a fact we must record since it had consequences after the German invasion in 1940. Ernest Kahane was born in Piatra Neamt, Romania, and became a university professor of biochemistry in France. A militant antifascist and communist, he was a member of the French Resistance during the German occupation of World War II. Ernest Kahane was the son of Albert Kahane (1872-1963) and Pépi Struhl (1879-1948). He became a French citizen on 15 February 1924 and he married the chemist Marcelle Wurtz on 27 December 1924 in Paris. Marcelle was the daughter of Georges Jean Wurtz and Henriette Mémé Moebs.

Jean-Pierre was the oldest of his parents three children, all sons. His two brothers were André Bernard Kahan (1929-) and Roger Kahane (1932-2013). Let us record here the following information about Jean-Pierre's brothers. André Bernard Kahan, born 14 November 1929 in Bois-Colombes, became a professor of physics at the University of Genoble. He is a member of the French Communist Party and a leading player of the game Go. Roger Kahane, born 20 December 1932 in Bois-Colombes, studied science but turned to film studies. He has directed many famous television series and films for the cinema.

Kahane attended the Lycée Henry-IV in the Latin Quarter on the left bank of the river Seine in Paris. This school, founded in 1796, was one of the most prestigious lycées in France. World War II had begun on 1 September 1939 with the German invasion of Poland. On 3 September France declared war on Germany. In May 1940 German troops invaded Holland, Belgium and Luxemburg moving on to France. German troops entered Paris on 14 June and on 22 June the Franco-German Armistice was signed. This limited the amount of France occupied by German troops and set up a French government in Vichy which cooperated with Germany. In Paris the occupying German forces began to move against Jewish members of the community and on 22 June 1940 they began to construct an internment camp at Royallieu-Compiègne. This camp, intended for French resistance fighters and Jews, was fully functioning by June 1941.

On his 15th birthday, 11 December 1941, Kahane was arrested at his parents' home in a raid by German soldiers. His father, realising the danger he was in as a Jew, had left Paris for the region controlled by the Vichy government. Kahane was taken to the Royallieu-Compiègne internment camp where Jews and communists were housed, separated by barbed wire. He was put on the Jewish side of the barbed wire but showed his political beliefs through quickly making contact with the communists. One might have expected this to lead to serious consequences for Kahane but, perhaps because of his young age, he was released on 18 December. The Germans occupied Paris from 1940 to 1944. The city was liberated in August of 1944.

In 1946, Kahane entered the École Normale Supérieure (ENS) and later that year he joined the branch of the Communist Party at the ENS. In the same year he joined the Mouvement Jeunes communistes de France (MJCF). We note that in fact the organisation only adopted this name in 1956 and, when Kahane joined, it was the Union de la jeunesse républicaine de France (UJRF). In 1947 he attended the 1st World Festival of Youth and Students held in Prague. The festival celebrated young people's solidarity for democracy and against war and imperialism. Kahane performed exceptionally well in his mathematical studies and graduated in 1949 ranked first in the mathematics aggregation.

Kahane joined the Syndicat National de l'Ensignement Secondaire (SNES) in 1947. This union for secondary school teachers had a long history but only adopted this name in 1944 after France was liberated. He became a researcher at the Centre National de la Recherche Scientifique (CNRS) in 1949. He had begun publishing mathematics papers in 1947 with Sur les propriétés des asymptotiques généralisées . This was followed by Quasi-analyticité des fonctions sommes de séries de Fourier lacunaires (1950), which he co-authored with Pierre Lalaguë, Extension du théorème de Carlson et applications (1952), and Quasi analyticité des fonctions moyenne-périodiques (1953).

On 11 July 1951, Kahane married Agnès Kaczander (1927-2014), the daughter of the engineer Maxime Kaczander of Hungarian origin, who was a communist student. They married in Paris and wished to spend their honeymoon in Hungary but were refused visas to enter Hungary. Jean-Pierre and Agnès Kahane had three daughters, Geneviève (born 1953), Françoise (born 1955) and Catherine (born 1960). Agnès was a translator who translated books from English and Hungarian into French.

In 1954 Kahane submitted his thèse de doctorat, Sur quelques problèmes d'unicité et de prolongement, relatifs aux fonctions approchables par des sommes d'exponentielles , to the Faculty of Science in Paris. His thesis advisor was Szolem Mandelbrojt. The authors of [5] write:-

In his thesis, he proposes a new theory of the medium-periodic functions of Delsarte and Schwartz, which surpasses and greatly simplifies the work of his predecessors.
After the award of his doctorate, Kahane was appointed as an assistant lecturer at the Faculty of Sciences of Montpellier, being promoted to professor in 1958. When he went to Montpellier, he accompanied his father Ernest Kahane who had been appointed to set up the teaching of biological chemistry at the Faculty of Sciences there. The family lived on rue Mareschal in Montpellier, in an apartment which had been given to them by the widow of the director of Midi Libre, Jacques Bellon, who was also of Romanian origin. Both Ernest and Jean-Pierre Kahane had common commitments: both were members of the French Communist Party. They were also members of the "Franco-Chinese Friendships" and the Rationalist Union of Montpellier which was chaired by Ernest Kahane.

Jean-Pierre Kahane travelled in Eastern Europe during the period of the Cold War, visiting Yugoslavia, Hungary, and Romania. He was also invited to teach at the Tata Institute in Bombay in 1957 and at the UNESCO Centre in Buenos Aires in 1959. Despite the crisis caused by the events in Hungary in the Revolution of 1956, he remained loyal to his party. The Revolution was led by Imré Nagy, a communist Hungarian politician but failed when the Soviet army invaded Hungary. Nagy was arrested, secretly tried, found guilty, sentenced to death and executed by hanging on 16 June 1958. This enraged Kahane who wrote (jointly with two colleagues) to János Kádár who was General Secretary of the Hungarian Workers' Party on 18 June 1958 (see [3]):-

We believe that it does not serve the anti-fascist cause, the popular cause, to let pass without protest what seems to us to be a new and serious mistake by the Hungarian authorities. Enemies in principle of the death penalty, anxious to see the basic rules of justice safeguarded - and in particular the right of accused to be defended, we cannot support the execution of Imré Nagy and his companions, under conditions which were stated to us: in closed session before the opening up of the proceedings, immediate execution of the sentence without the possibility of appeal or of grace. We are convinced that a socialist democracy can be imposed without resorting to such methods.
The Algerian war of independence began on 1 November 1954. The mathematician Maurice Audin, a member of the Communist Party of Algeria which he joined in 1950, strongly supported Algeria's right to be independent of France. He was murdered by the French authorities but, after a long argument about the circumstances of his death, Audin's thesis was accepted posthumously on 2 December 1957 with an in abstentia defence at the Sorbonne. Kahane was a strong supporter and attended Audin's in abstentia defence. Kahane published an article on 8 February 1958 in which he retaliated to attacks on academics by journalists, writing about the [3]:-
... crimes committed under the guise of the Algerian war. ... You will not impose silence on academics by calling them traitors and morons.
In 1961, the Communist Federation of Herault created a "New University" in Montpellier, housed Rue des Étuves, presided over by Jacques Roux, and which began with 110 communist sympathisers including Kahane and his father. Kahane, however, was about to leave Montpellier for, in 1961, he was appointed Professor at the Faculty of Sciences of Paris Sud at Orsay. He served as President of the University from 1975 to 1978. He remained a professor at Orsay for the rest of his career until he retired in 1994.

On 29 July 1961 Kahane flew from Paris to New York, USA, to spend four weeks at Stanford University departng on 26 August. He gives his Paris address as 11 rue du Val-de-Grâce, Paris.

Soon after arriving back in Paris he joined the Syndicat National de l'Enseignement Supérieur (SNESup). This union had come into existence in 1956 and had a reputation as being on the political "left". Michel Chaillou, the Secretary General, invited Kahane to join the office of the union and Kahane served as the next General Secretary 1961-62 and again 1963-64. He attended the International Congress of Mathematicians held in Stockholm, Sweden, from 15 August to 22 August 1962. He had been invited to deliver a one hour plenary lecture at the Congress and delivered Transformées de Fourier des fonctions sommables . He gave the following introduction to his lecture:-

In Fourier analysis, there are probably few more natural questions than the study of Fourier transforms of summable functions. This includes, in particular, the functions, continuous on the circle, whose Fourier series is absolutely convergent (Fourier transforms of summable functions on the group of integers), and the Fourier-Lebesgue coefficient sequences (Fourier transforms of summable functions on the circle). The subject, although long studied, remained rather mysterious: in 1958, in the introduction to the second edition of his treatise, Zygmund counted, among the two or three major problems concerning the trigonometric series, that of specifying the structure of the functions having absolutely convergent Fourier series. In recent years, and particularly since 1958, important progress has been made: long-sought problems have been solved; others have arisen. I would like to try to give an overall picture here, hoping that many of the delegates will have been able to hear the most remarkable recent results directly from the authors (I think, in particular, of Paul Malliavin and Paul J Cohen). Interested mathematicians can also refer to the excellent work of Walter Rudin, which will appear shortly.
He was a member of the Central Committee of the Communist Party from 1979 to 1994, in charge of issues relating to science, research and new technologies. He said (see for example [3]):-
I have been a communist since the age of twenty. I was a grassroots activist, a member of a cell, a platoon, without any significant responsibility, until I was "shoved" as a member of the Central Committee. It was in 1979. Based on me looking good and my performance as university president, I guess. But in fact there was something to be done to the Communist Party. The Communist Party has strong traditions in relation to science, with personalities who have marked it strongly like Paul Langevin, like Frédéric Joliot-Curie, and previously like Marcel Prenant. Now, there is a need to constantly reactivate, whether in the Communist Party or elsewhere, this interest in science.
He took on other roles such as president of the Inter-Ministerial Mission for Scientific and Technical Information from 1982 to 1986 and president of the Rationalist Union from 2001 to 2004. He also chaired the International Commission on Mathematical Instruction of the International Mathematical Union from 1983 to 1990 and the National Mathematical Education Commission from 1997 to 1999.

MathSciNew lists nearly 300 publications by Kahane. Giving an overview of these would be impossible so let us look at some of the important books he published. We mentioned above that he taught at the UNESCO Centre in Buenos Aires in 1959. Two resulting sets of his lecture notes were published in 1961, namely Algebras de convolucion de sucesiones, funciones y medidas sumables and Teoria constructiva de funciones . In 1963 his book Ensembles parfaits et séries trigonométriques (co-authored with Raphaël Salem) was published. R P Boas writes in a review:-

This elegant book treats a variety of topics in the theory of trigonometric series - some fairly well known, but most of them quite recent - unified by the occurrence in each case of special classes of perfect sets.
Kahane's book Séries de Fourier aléatoires (1963) was reviewed by H Hever who writes:-
This is a set of lecture notes on the highly interesting subject of random Fourier series. The reader is first introduced to the elementary theory of Fourier series (and also to the notion of hyperdistribution, invented in 'Ensembles parfaits et séries trigonométriques' by the author and R Salem) as well as to the elements of probability theory. Here one can find a natural proof of the famous Marcinkiewicz-Zygmund result on almost sure convergence of sums of independent real random variables after translation by a suitable sequence of real numbers. As an application, the equivalence principle for sums of independent real random variables is given. ... Altogether the set of notes under review is a most desirable aid for any introduction to the "pearls" of the theory of random Fourier series.
His next book Some random series of functions (1968) is described by Paul Erdős as:-
... an interesting little book [which] deals with various problems and results on random series. ... The book can be recommended very highly to those who want to do further research in this interesting field, which may have many new and unexpected potentialities and to which the author has made many important contributions.
The International Congress of Mathematicians was held in Nice, France from 1 September to 10 September 1970. Kahane was a member of the Organising Committee of this Congress.

He was elected a corresponding member of the Académie des Sciences in 1982, and elected a full member on 5 January 1998. He was President of the French Mathematical Society in 1972-1973. He was elected to the Polish Academy of Sciences and the Hungarian Academy of Sciences. He received numerous awards including the Peccot prize at the Collège de France in 1957, the Servant prize in 1972, the prix d'État des sciences mathématiques et physiques in 1980, the Maurice Audin prize, the Émile Picard medal from the Académie des sciences in 1995, and several more.

His funeral, which took place on 30 June 2017, was attended by a large number of people. He was buried at the Père Lachaise cemetery.

Jean-François Le Gall and Cédric Villani write [5]:-

Jean-Pierre Kahane was one of the great mathematicians of the late twentieth century, an emblematic figure during several decades of French harmonic analysis. Thanks to his extraordinary inventiveness, he has discovered many brilliant and profound results in mathematical analysis as well as in probability theory. But Jean-Pierre Kahane will also remain an outstanding character for his action in the service of the community and his political commitment to "change the world" as he said himself.
Let us end with two quotes by Kahane, given in [2]:-
I am a professional mathematician, a good mathematician. But I am also an amateur: I like to discover what others do, and I also like to flutter. At my age, I will be less and less professional. I hope to be more and more an amateur, an amateur of all that is beautiful and useful in the mathematics of the past and present.

As a researcher, I felt more like a gardener than an architect. So I helped to discover or create new species, which sometimes seem strange before we get used to them. However, my activity as a researcher did not follow an overall plan: I was carried by open questions, asked by my teachers, by colleagues or by chance through my reading. In each case it needed ad hoc tools, and the pleasure, as in any business, was that the tools worked well. We know that there is no pleasure without pain, and I have struggled a lot, as everyone probably has, by going astray, deceiving myself, correcting, starting again, before ending up with results that gave me the most pleasure.
In May 2017, he wrote in L'Humanité:-
False beliefs prevent society from advancing on pressing issues ... The progress of science, progress in medicine, all the progress that we can think of, translate and aggravate the inequalities in the world. They could be for the benefit of all, but they are first of all at the service of the rich and powerful.

Article by: J J O'Connor and E F Robertson


List of References (6 books/articles)

Mathematicians born in the same country

Cross-references in MacTutor

  1. 1970 ICM - Nice
  2. 1986 ICM - Berkeley

Other Web sites
  1. Mathematical Genealogy Project
  2. MathSciNet Author profile
  3. zbMATH entry


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