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Debate surrounds $25000 prize won by undergraduate for
universal Turing machine problem
CAPTCHA if they can
A test invented by the mathematician Alan Turing in 1950 is helping to stop spammers.
What computers can't do
looks at the life and work of wartime code-breaker Alan Turing. Find out what types of numbers we
count and why there are limits on what can be achieved with Turing machines.