Thanks, Owen. It helps a lot:)
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Jill,
The old PRE never really worked properly, or at least was never
really finished. We're planning to implement GVN-PRE (ftp://
ftp.cs.purdue.edu/pub/hosking/papers/vandrunen.pdf) as it is a more
powerful algorithm. You are right, of course, that the ability of
the PRE to determine the equivalence of two expression. This is an
area that can always be improved, and it's mostly an issue of if it's
worth the amount of work required to prove a given equivalence. This
is something that'll probably have to be determined empirically.
Hope this help,
--Owen
