On 6/6/09, Dieter Kaiser <drdieterkaiser at web.de> wrote:
> That is the most difficult point. What solution would be general and
> correct. Furthermore, I think it is very useful to have a simple
> concept.
Well, [] is a little too simple: it doesn't have any indication
about the problem; you have to know that [] was unexpected
to know there was a problem at all.
> As written in another posting, I am not convinced that we get into
> conflicts with the interpretation "No solution" in a context where we
> want to solve an integral.
Why invent this special convention at all? Why go to the
trouble of it, when we can just as easily have a symbol
or expression which explicitly indicates an error?
> By the way: I am thinking about a way to support the user with
> additional information about the calculation. One way could be to write
> messages in a global list, which can be inspected by the user.
I'm opposed to this. If there is some information which is known,
just smash it into the return value somehow. If it is too verbose,
attach it to the property list.
> Perhaps, an automatic mapping which depends on the value of listarith
> might be useful to get the mapping of functions more consistent to the
> mapping of the arithmetic operators. It is easy to implement and could
> be done step by step.
If "step by step" means hacking the simplifier in each of the places
which we can find, then that's exactly what I want to avoid.
best
Robert Dodier