A handwritten notebook in which Britain 's Enigma machine genius Alan Turing admits he is baffled by an equation could fetch up to $ 1million ( £690,000 ) . The 56-page book bought in Cambridge contains Turing 's thoughts on the clearly tricky 'Leibniz notation dx/dy ' . ' I find [ it ] extremely difficult to understand in spite of it having been the one I understood the best once ! ' he wrote . Scroll down for video . A handwritten notebook in which Britain 's Enigma machine genius Alan Turing admits he is baffled by an equation could fetch up to $ 1million ( £690,000 ) . Above , he wrote that the Leibniz notation was 'extremely difficult ' It was written at the Bletchley Park code-breaking headquarters in 1942 and paved the way for computer science . It is believed to be the only extensive Turing manuscript known to exist , the auctioneer said . Benedict Cumberbatch , who played Turing in the Oscar-nominated The Imitation Game , said : 'Alan Turing was a war hero , who broke the Enigma code helping to bring an end to World War II , the father of modern computing science , and a gay icon who lived in a time of intolerance and tragically committed suicide as a result . 'His impact on our everyday lives is enormous , and the thought of holding a manuscript by him is thrilling . ' The notebook was among the papers he left in his will to friend and fellow mathematician Robin Gandy . Turing ( left ) wrote the notes at the Bletchley Park code-breaking headquarters in 1942 and they paved the way for computer science . The notes are believed to be the only extensive Turing manuscript ( right ) known to exist , the auctioneer said . Pages of notes show the inner workings of Turing 's thoughts as he helped break codes and decipher tests . The notes , which are highly personal , show Turing working through different equations and considering different results . Gandy gave the papers to The Archive Centre at King 's College in Cambridge in 1977 . But he kept the notebook , using its blank pages for writing down his dreams at the request of his psychiatrist . Bonham describes Gandy 's entries as highly personal ; the notebook remained in his possession until he died in 1995 . At the beginning of his journal , Gandy writes : 'It seems a suitable disguise to write in between these notes of Alan 's on notation , but possibly a little sinister ; a dead father figure , some of whose thoughts I most completely inherited . ' In a statement through Bonhams , Turing scholar Andrew Hodges said the notebook sheds more light on how Turing 'remained committed to free-thinking work in pure mathematics . ' Benedict Cumberbatch , who played Turing in the Oscar-nominated The Imitation Game ( left ) , said : 'The thought of holding a manuscript by him is thrilling ' In some Turing elaborates on his conclusions , writing that one result 'is too subtle and makes an inconvenient definition ' He added : 'Alan Turing was parsimonious with his words and everything from his pen has special value . ' Turing committed suicide in 1954 . He was gay at a time when homosexuality was illegal in Britain and was convicted of indecency in 1952 . He agreed to undergo hormone treatment as an alternative to imprisonment to 'cure ' his homosexuality . It will be sold by Bonhams in New York on Monday . It said the seller wished to remain anonymous . Part of the proceeds will be donated to charity .
56-page book contains Turing 's thoughts on tricky 'Leibniz notation dx/dy ' It was written at the Bletchley Park code-breaking headquarters in 1942 . Only extensive Turing manuscript thought to exist , the auctioneer said . It will be sold by an anonymous seller by Bonhams in Britain on Monday .