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Alan Turing's notebook goes on display at Bletchley Park

Alan Turing Image copyright Science Photo Library
Image caption Alan Turing's work helped Allied efforts to read secret German messages sent by their Enigma machines

A notebook owned by World War Two codebreaker Alan Turing has gone on display.

The 39-page book was privately bought for $1m in New York and is on loan to Bletchley Park in Buckinghamshire.

Notes on Notations was written while Turing was cracking German codes and provides a commentary of the language of mathematics.

Sir Dermot Turing said the manuscript revealed his uncle had a sense of humour and was not "a total geek."

'Somewhat deplored'

He said: "It's quite clear he saw the code-breaking activity as a sort of fun pursuit to be fitted in around the intervals of doing what he considered to be his real profession, which was academic mathematician.

"It's very different from the whole Enigma story that he was working on at the same time."

BBC iWonder - Timeline of Alan Turing's life

Image copyright Chris Radburn/PA
Image caption The notebook was written while Turing worked on deciphering codes

The notebook is one of just a handful of Turing's written manuscripts in existence.

In it, he regards some mathematical formulae written by his contemporaries as "ugly" and "somewhat to be deplored".

Sir Dermot said the subject matter provided no psychological insight in to Turing.

But he added: "You do get a sense that this is not somebody who's a total geek, even though what he's doing is working on something that's really quite technical."

Image copyright Chris Radburn/PA
Image caption The notebook reveals Turing's wry approach to the work of his contemporaries

The notebook had been left with close friend and student Robin Gandy. It was sold to an anonymous buyer in April 2015.

Dr David Kenyon, research historian at Bletchley Park, said it was hard to overestimate the importance of Turing's codebreaking techniques, which appeared to be a "hobby on the side".

He said: "Turing is thinking about something else a lot of the time... but he was able to turn some of that genius to codebreaking as and when required."

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