The famous "Solitaire letter" sent by Alan Turing to the daughter of his psychologist is valued at £40,000-60,000 ($61,737-92,605) ahead of a sale at Bonhams.
It's among the lead lots of a sale of books and literary memorabilia on June 24.
Turing began visiting Dr Franz Greenbaum in the last months before his suicide. The two men became friends and Turing would often sit with Greenbaum's daughter and play Solitaire.
The letter is dated July 10, 1953 and explains in detail the moves needed to win the game.
Maria told the Daily Mirror in a 2014 interview: "I grew very fond of him and he was always very friendly. He eventually became more of a family friend than a patient of my father.
"I remember him having dinner with us often. After dinner he would sit on the floor with me while I played Solitaire. I thought it was so nice.
"He was a very warm person who always took an interest in what I was doing. I grew very attached to him... He had quite a stammer and bit his nails. He could be described as hyped up. But I always remember him as kind and friendly."
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