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Concerning the review of Impossibility by John Barrow, ("Taking it to the limits" THES, September 4), one lesson of a survey of theories of impossibility in the sciences must be that declarations of supposed impossibility may delay discovery, in the cases where solutions in fact exist. After failure to solve a problem, theorists may explain that a solution was impossible; if this is accepted then research to solve a problem is likely to be reduced.

Alexander Chablo Manchester