The EP has five songs which are entirely different, which makes the trio difficult to categorise.

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The Ugandan-born churchman has espoused a weird variety of causes, making him impossible to categorise.

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Dr Caglioti and his colleagues have created a program that can categorise documents by language or authorship, based on these extra lengths.

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They also ask potential users to carry out card sorting exercises to see how they categorise and classify the subjects on a website.

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He said that because there are many different types of schizophrenia, which are treated in many different ways, it is difficult to categorise patients.

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Essentially Pearltrees users are helping to explore and categorise the web.

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Recent research from charity Age UK, looking at how Europeans categorise themselves, found the average age at which old age is perceived to start is 62.

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But the document belongs to a long tradition of those who have felt compelled, like Father Christmas, to categorise those whom they consider to be "naughty" rather than "nice".

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In any event, if the majority of world opinion remains opposed to military action, it is likely to be difficult on the facts to categorise a French veto as "unreasonable".

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It is unfair to categorise Syrian plans for irrigation as a waste of water when Turkey plans much more, yet has a climate better suited to rain-fed agriculture than Syria's or Iraq's.

ECONOMIST: Letters