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Most people realise that all software contains bugs - and even Mathematica \
contains a few. For example, at version 5.0 the following double integral
evaluated incorectly to zero:\
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 "This was indeed a bug at version 5.0 - happily cleared at version 5.1. \n\n\
Some people react to a discovery of this sort by asking how they can ever \
trust Mathematica again! However, this is very simplistic. Mathematica will \
make far fewer mistakes that almost any human mathematician. Furthermore, \
even if ",
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 " were a perfect piece of software, you could still make mistakes because of \
'bugs' in your input. For example, consider this:"
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Cell["\<\
I am sure Wolfram support have received assorted variants of that 'bug' from \
time to time, but if you look carefully, there is no space between the 'x' \
and 'y' variables - thereby creating a new variable 'xy' -  so this is simply \
the indefinite integral of a constant.

Thus, you must proceed cautiously before doing something irreversible (such \
as publishing a paper!) using a result. This is obviously doubly true if a \
result looks surprising. Do exactly what you might do in a hand calculation - \
check the result in a totally independent way. The above double integral \
could have been evaluated in two stages using 1-D integration, or it could \
have been evaluated numerically using NIntegrate for randomly chosen values \
of the other constants. Either experiment would have revealed the error. 

Mathematica bugs (at least in the kernel) are pretty rare, but so are hard \
disk failures, but that is hardly a reason not to take a back-up disk copy!\
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