[Axiom-developer] exquo issue

[Martin Rubey]

Dear all,

as you may have noticed, 

exquo(simplify((A-2^a)*(A+2^a))::UP(A,EXPR INT),(A-2^a)::UP(A,EXPR INT))

currently fails. The reason is that Axiom does not know that

simplify((2^a)^2-2^(2*a))

vanishes.

Of course, that problem is unsolvable in general. However, I'm quite sure that
the current way deals with the problem (it ignores it) is that good.

I see the following possibility:

Every domain (that has a zero element) should know whether it can determine
whether one of its members is zero or not.

If it cannot, it should implement heuristics, but emit a warning.

Opinions?

Martin