I wrote:
>
> Slawomir Kolodynski wrote:
> >
> > Suppose I have an expression like *(y-m)*sqrt(x)/s* . What I would like to
> > do is to give a name *e* to the *sqrt(x)/s* part and do some kind of
> > transformation on this expression so that I get *(y-m)*e *or equivalent as
> > the result*. *To do that I define a rule
> >
> > substE := rule (('y-'m)*sqrt('x)/'s == ('y-'m)*'e)
> >
> > However, when I try to apply this rule to the expression
> >
> > substE (y-m)*sqrt(x)/s
> >
> > I get the *(y-m)*sqrt(x)/s *expression back instead of *(y-m)*e. *It looks
> > like the left hand side of the equality in the rule substE does not pattern
> > match itself.
>
> Yes. In expression numerator is a sum, that is what you really
> have is:
>
> y*sqrt(x) - m*sqrt(x)
>
> In pattern (to which left hand side of the rule is converted) we
> have product. Product does not match sum... I need to check
> is this is just a bug or an unavoidable misfeature.
AFAICS the problem is in convertion from polynomials to patterns.
Looks like a bug, but attempting to fix it showed other
problems with rules, so I need to dig deeper.
--
Waldek Hebisch
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