> Sorry if this is a very short explanation but you will find a longer one in
> my book....

It seems we need an online version of your book!
(Seriously - I know some books that are available online completely
*and* in printed form, though I don't know how this biased the sales)

Cheers,
Oliver

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|  ob|do        Dipl.Inf. Oliver Becker                             |
|  --+--        E-Mail: obecker@xxxxxxxxxxxxxxxxxxxxxxx             |
|  op|qo        WWW:    http://www.informatik.hu-berlin.de/~obecker |
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