Martin Rubey <[EMAIL PROTECTED]> writes:
> Waldek Hebisch <[EMAIL PROTECTED]> writes:
>
> > I am now cleaning patch changing attributes to categories. AFAICS
> > the following attributes are essentially unused:
> >
> > leftUnitary
> > rightUnitary
> > NullSquare
> > JacobiIdentity
> > infinite
> > noetherian
> > central
> > unitsKnown
> > canonicalsClosed
> > canonical
> >
> > By essentially unused I mean that they are only defined and not
> > used or are used only in its own definition or definition of
> > another essentially unused attribute.
> >
> > Most of then look like mostly unimplemented. Also, most of them
> > does not look really useful. I am tempted to remove to first 7 of
> > them. The last 3 look like they may be of some use so ATM it
> > is not clear what to do with them.
>
> I agree.
Oops, sorry, I changed my mind. I thought they would only appear in attreg,
but they don't: they document an attempt to encode more mathematical knowledge
in the algebra.
If it's not more work, please leave them in (replacing them with empty
categories). Possibly one can use them at some point.
I do think, however, that the "canonical" attributes are either badly
documented or exported by mistake. For example:
canonicalUnitNormal
++ \spad{canonicalUnitNormal} is true if we can choose a canonical
++ representative for each class of associate elements, that is
++ \spad{associates?(a,b)} returns true if and only if
++ \spad{unitCanonical(a) = unitCanonical(b)}.
and in Field (!) we have:
canonicalUnitNormal ++ either 0 or 1.
canonicalsClosed ++ since \spad{0*0=0}, \spad{1*1=1}
But this seems wrong to me, since EXPR INT is a Field (and I think this is
correct if we look at expressions as functions), but we cannot decide whether
something is identically zero.
As a use case, I could imagine that algorithms that only "really" work for
domains where one can test for zero spit out a warning.
Martin
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