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14 April 2015, 06:20 | Updated: 14 April 2015, 06:23
A notebook belonging to Bletchley Second World War code-breaker Alan Turning has been sold at auction for almost £700,000.
The paper, in which he details his work on the foundations of mathematical notation and computer science, was sold for $1,025,000 (£698,000) in a Fine Books & Manuscripts Sale at Bonhams in New York, the auction house confirmed.
Turing is best known for his contribution to cracking the code used by the Germans in their Enigma machines during the Second World War when he worked for the Government Code and Cypher School at Bletchley Park.
He is often said to be the father of modern computing and artificial intelligence.
But Turing died from poisoning in 1954, generally thought to have been an act of suicide as a consequence of the hormone treatment he was undergoing as an alternative to imprisonment for his homosexuality.
Prime Minister Gordon Brown apologised on behalf of the British Government in 2009 for the way Turing had been treated and he was granted a posthumous pardon in 2013.
His story was featured in the Oscar-nominated movie The Imitation Game last year, starring Benedict Cumberbatch.
Bonhams said a rare three-rotor German Enigma Enciphering Machine sold at the same auction for a world record price of $269,000 (£183,000).
Cassandra Hatton, senior specialist in Fine Books and Manuscripts and the History of Science at Bonhams, said the Turing manuscript was among the papers left in his will to his close friend and fellow mathematician, Robin Gandy.
She said it is made up of 56 pages in a simple notebook bought from a stationers in Cambridge and is almost certainly the only extensive autograph manuscript by Turing in existence.
It is thought to date from 1942 when Turing was working at Bletchley Park.
Part of the manuscript reads: "The Leibniz notation Image removed by sender. I find extremely difficult to understand in spite of it having been the one I understood the best once! It certainly implies that some relation between x and y has been laid down eg, y=x2+3x...''
Ms Hatton said: "This is a wonderful result and a fitting testament to Alan Turing's impact and legacy. It has been a great privilege to have been involved in this sale and we are immensely pleased that all the people who bid for this unique item and indeed the wider public have recognised Turing's importance and place in history.''
A portion of the proceeds from Bonhams and the vendor will be donated to charity, the auctioneers said.