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Re: Replacement Rule with Sqrt in denominator

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  • Subject: [mg114392] Re: Replacement Rule with Sqrt in denominator
  • From: Richard Fateman <fateman at>
  • Date: Fri, 3 Dec 2010 05:19:36 -0500 (EST)
  • References: <ic5igm$44p$> <ic8ad7$81f$> <id7t95$lh1$>

On 12/2/10 2:43 AM, Roland Franzius wrote:

The paper I wrote, previously mentioned in this thread, suggests and 
implements an alternative rule matching process, and provides an
alternative syntax for it,  namely

a =/. r
where r is a rule and a  is an expression.

It fixes the bugs that appear to exist, to many users, when they use
a  /. r

Thus it is not necessary to look at FullForm, nor is it necessary
to declare a bug a feature.

Now you may not like this alternative pattern matching process
either, but to declare that it is impossible to do this Sqrt[]->...
thing is obviously wrong.

Now DanL's view (restated somewhat) that this constitutes the
thin edge of the wedge of expecting Mathematica to "read my mind"
has some validity.  How much more (beyond what is in that paper)
should be done?  Is the treatment of a+b*I  and negative powers
all that is needed?  It would go a long way to eliminating the
frustration exhibited by people who took the effort to report their
problems to this newsgroup, and who were sophisticated enough to
actually report it.  (Uh, maybe not so much these days, where
infants send text messages from cribs...)

Anyway, I would rather have the CAS do some simple guessing of what
I mean, as at least a fair trade for me having to guess what secret 
things will happen in FullSimplify or Integrate or Solve,  or ...
especially as versions change.  I do recall that this community
experienced  (at least once) a minor uprising of people who refused
to upgrade to the next higher version, on the grounds that the new
version introduced uh, bugs. or were they features.

Basically, explaining a bug does not make it into a feature, especially
when it can actually be fixed.


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