Re: [Axiom-developer] fixing SPAD

[Waldek Hebisch]

Martin Rubey wrote:
> Dear Gaby & Waldek,
> 
> as you may know, there is a problem fixing bug #354, Complex R is not
> necessarily a field when R is a field.
> 
> It would be quite straightforward to fix it, if we could conditionally export
> Field, depending on a Boolean valued function, like
> 
> if R has Field and R has Finite and size()$R rem 4 = 1 then Field
> 
> Currently, spad seems to accept statements of the form
> 
>    D has C
> 
> and
> 
>    D1 is d2
> 
> only.  (Please check this, I'm not entirely sure.)  Do you think it would be
> difficult to fix this?  I do not see a workaround, unfortunately.
> 

For issue 354 I belive that there is reasonable workaround: just export
Field unconditionally (as we do know), but throw error when sombody
tries to create a fake field.  For example PrimeField is doing this --
it exports Field for any value of p, but complains if you give it
non-prime p.

I belive that we should add to Complex something like the snippet below
(untested, ATM I am busy with other things)

   == add
      if R has Field then
         if R has complex or _
            ((characteristic()$R) mod 5 = 1) or _
            (R has Finite and _
               ((size()$R) mod 5 = 1) then
           error "Field given to Complex already contains square root of -1"


-- 
                              Waldek Hebisch
address@hidden