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Re: Re: When is a List not a List?

• To: mathgroup at smc.vnet.net
• Subject: [mg90993] Re: [mg90956] Re: [mg90947] When is a List not a List?
• From: Andrzej Kozlowski <akoz at mimuw.edu.pl>
• Date: Sat, 2 Aug 2008 03:26:40 -0400 (EDT)
• References: <200807310656.CAA07700@smc.vnet.net> <16711231.1217501820078.JavaMail.root@m08> <op.ue54zeqq2c6ksp@bobbys-imac> <21465667.1217530845998.JavaMail.root@m08> <op.ue6m0tdk2c6ksp@bobbys-imac> <32926975.1217563920588.JavaMail.root@m08> <op.ue7o67wi2c6ksp@bobbys-imac> <97345FCA-2165-4054-A869-BA4F30AA8450@mimuw.edu.pl> <10968735.1217609075862.JavaMail.root@m08> <op.ue72ktyw2c6ksp@bobbys-imac>

On 1 Aug 2008, at 21:18, DrMajorBob wrote:

> In light of all that, in what way have the rest of us failed to  
> understand "a bit of mathematics"?

Te bit of mathematics (and computer algebra) you clearly do not  
understand is the very basic fact when you solve many kinds of  
algebraic equations with symbolic parameters you inevitably introduce  
parasite solutions. When you use numeric parameters Solve can verify  
which of theses are correct. The rest of the discussion is totally  
besides the point, and so is using Reduce (for example, because one  
can easily come up with equations that Reduce will not manage).
The example was meant to illustrate the very trivial and elementary  
fact that the world is full of functions with parameters that can be  
evaluated pointwise (once numeric parameters have been substituted)  
but cannot be evaluated by Evaluate. This is so basic and there are so  
many examples of it that I do not see any point in discussion this  
farther.

Andrzej Kozlowski