But it would offer a way to make better raincoats, and is also a proof of principle.

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These results are a proof of principle and a demonstration of huge potential.

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Peter Harrison, the firm's chief executive, told BBC News that the demonstration did not focus on efficiency, but rather a proof of principle.

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As a proof of principle, that is not bad.

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At that stage Dr Pusztai's research simply looked like a proof of principle checking that the techniques for transplanting and testing lectin genes worked, prior to exploring other, less harmful lectins as built-in insecticides for crops.

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Although Yurke's tweezers are just a proof-of-principle, similar molecular motors might be used to assemble very tiny computer chips.

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Such an experiment is somewhat ad hoc but should at least provide a proof-of-principle, according to Jim Tartaglia , global head of HIV research at Aventis.

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Dr Lorenz Studer, head of the Stem Cell and Tumor Biology Laboratory at the centre, and the lead researcher on the study, told BBC News Online that the study was "proof of principle" that cloned embryonic stem cells could be reliably transformed into a variety of useful cell types.

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