This is a classical example that combines lazy (actually the real name is non-strict) lists and recursion.<br>
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You can find an explanation of such a combination here<br>
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<a href="http://stackoverflow.com/questions/6273621/understanding-a-recursively-defined-list-fibs-in-terms-of-zipwith">http://stackoverflow.com/questions/6273621/understanding-a-recursively-defined-list-fibs-in-terms-of-zipwith</a><br>
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Silvio