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I was aghast at last week's Don's Diary. So it took mathematicians 125 to prove that we need four colours to colour all mugs and that they are still working on a non-computer solution. This really is untenable.

I hope the secretary of state for education, himself an ex-mathematician, sets clear targets for improvement - 125 years is too long and four colours are just too many. Let's set a target of getting it down to three colours by 2010. Good heavens, there was a time when one colour was enough to colour most of the world!

Peter Gates
University of Nottingham