Question: Who is older, Julian Barnes or Arthur Koestler?

Context paragraphs:
Arthur Koestler (book): "Arthur Koestler" is a book by Mark Levene published in 1984, a year after Arthur Koestler's suicide.  The book is divided into seven main chapters, of which the first of is a biography and the other six critical essays on each of Koestler's six novels, his stories and his play "Twilight Bar".

Holarchy: A holarchy, in the terminology of Arthur Koestler, is a connection between holons, where a "holon" is both a part and a whole.  The term was coined in Koestler's 1967 book "The Ghost in the Machine".

Holon (philosophy): A holon (Greek: "ὅλον, holon" neuter form of "ὅλος, holos" "whole") is something that is simultaneously a whole and a part.  The word was coined by Arthur Koestler in his book "The Ghost in the Machine" (1967, p. 48).  Koestler was influenced by two observations in proposing the notion of the holon.  The first observation was influenced by Herbert A. Simon's parable of the two watchmakers—in which Simon concludes that complex systems evolve from simple systems much more rapidly when there are stable intermediate forms present in the evolutionary process than if they are not present.  The second observation was made by Koestler himself in his analysis of hierarchies and stable intermediate forms in non-living matter (atomic and molecular structure), living organisms, and social organizations.  He concluded that, although it is easy to identify sub-wholes or parts, wholes and parts in an absolute sense do not exist anywhere.  Koestler proposed the word holon to describe the hybrid nature of sub-wholes and parts within in vivo systems.  From this perspective, holons exist simultaneously as self-contained wholes in relation to their sub-ordinate parts, and as dependent parts when considered from the inverse direction.

Spanish Testament: Spanish Testament is a 1937 book by Arthur Koestler, describing his experiences during the Spanish Civil War.  Part II of the book was subsequently published on its own, with minor modifications, under the title "Dialogue with Death" (see below).  Koestler made three trips to Spain during the civil war; the third time he was captured, sentenced to death and imprisoned by the Nationalist forces of General Franco.  Koestler was at that time working on behalf of the Comintern and as an agent of the Loyalist Government's official news agency, using for cover accreditation to the British daily "News Chronicle".

Arthur Koestler: Arthur Koestler, ( ; ] ; Hungarian: "Kösztler Artúr" ; 5 September 1905 – 1 March 1983) was a Hungarian-British author and journalist.  Koestler was born in Budapest and, apart from his early school years, was educated in Austria.  In 1931 Koestler joined the Communist Party of Germany until, disillusioned by Stalinism, he resigned in 1938.  In 1940 he published his novel "Darkness at Noon", an anti-totalitarian work that gained him international fame.  Over the next 43 years, from his residence in Britain, Koestler espoused many political causes, and wrote novels, memoirs, biographies and numerous essays.  In 1968 he was awarded the Sonning Prize "for [his] outstanding contribution to European culture" and in 1972 he was made a Commander of the Order of the British Empire (CBE).  In 1976 he was diagnosed with Parkinson's disease and in 1979 with terminal leukaemia.  In 1983 he and his wife committed suicide at their home in London.

The Encyclopœdia of Sexual Knowledge: The Encyclopaedia of Sexual Knowledge, under the editorship of Dr. Norman Haire (1892–1952), is the first of a trilogy of sexual encyclopaedias by Arthur Koestler writing under the pen name of ‘Dr. A. Costler’.  It is the English version, published by Koestler's cousin Francis Aldor in 1934, of the book "L'encyclopédie de la vie sexuelle" that Koestler in 1933 wrote, together with "A. Willy" (the pseudonym of his other cousin Willy Aldor) and the German Dr. Levy-Lenz.  The second book is "Sexual Anomalies and Perversions, Physical and Psychological Development, Diagnoses and Treatment".  The title of the third book is, in the original French edition of 1939, "L’Encyclopédie de la famille".  This third book was subsequently translated into English and published under various titles and with changes to the structure and text of the original edition.  The name of ‘Dr. Costler’ (or 'A. Coester') as the author or co-author of the book is omitted from later editions.

Stranger on the Square: Stranger on the Square is the third volume of Arthur Koestler's autobiography, published posthumously in 1984.  It was co-authored with his wife Cynthia Koestler, née Jefferies, and includes autobiographical notes of her as well.  The book was published by Hutchinson, London 1984, 242 pages including Index.  ISBN  .  It was edited by Harold Harris, who wrote the Introduction and Epilogue.  He was Koestler's editor for many years.  The book is illustrated with seven monochrome photographs plus a colour and another momochrome photograph on the dustcover.

Arthur Koestler: The Story of a Friendship: Arthur Koestler: The Story of a Friendship is a book by George Mikes published in 1983, soon after Arthur Koestler’s suicide.  As the author states in the Introduction, the book is not a biography of the subject but a series of recollections and anecdotes of a friendship spanning more than thirty years from 1952 up to the time of Koestler’s suicide in March 1983.

Julian Barnes: Julian Patrick Barnes (born 19 January 1946) is an English writer.  Barnes won the Man Booker Prize for his book "The Sense of an Ending" (2011), and three of his earlier books had been shortlisted for the Booker Prize: "Flaubert's Parrot" (1984), "England, England" (1998), and "Arthur & George" (2005).  He has also written crime fiction under the pseudonym Dan Kavanagh.  In addition to novels, Barnes has published collections of essays and short stories.

Living with Koestler: Living with Koestler: Mamaine Koestler's Letters 1945–51 is a book about the author Arthur Koestler and Mamaine Paget, Koestler’s second wife.  More specifically, it is a selected compilation of Mamaine’s letters to her twin sister Celia about her life with Koestler.  The spontaneous and engaging letters reflect the intensity of her life with Koestler between 1945 and 1951.

Supporting paragraphs: Julian Barnes Arthur Koestler
Answer: Arthur Koestler