That definitely is not a bug in CombinatorialFreeModule, so there shouldn't
be anything changed there. It is doing what it is told: that its indexing
set is in finite sets. I would say the bug is purely in the
DisjointUnionEnumeratedSets not doing a full check of its member sets.
Best,
Travis
On Saturday, June 20, 2020 at 8:43:06 PM UTC+10 hel...@potuz.net wrote:
> On Jun 20, Markus Wageringel wrote:
> >I think the problem here is that enumerating over a disjoint union of an
> >infinite set and a finite set will never reach the elements in the finite
> set.
> >There is this comment in the documentation of DisjointUnionEnumeratedSets
> >
> >
> > Possible extensions: the current enumeration order is not suitable
> > for unions of infinite enumerated sets (except possibly for the
> > last one). One could add options to specify alternative enumeration
> > orders (anti-diagonal, round robin, ...) to handle this case.
> >
> >
> >so the workaround is to first enumerate over the finite set and then the
> >infinite set, as the last enumerated set in the union will determine
> whether
> >the disjoint union is finite or not:
> >
> >sage: DisjointUnionEnumeratedSets([NonNegativeIntegers(), Family('x')])
> in
> >FiniteSets()
> >True
> >sage: DisjointUnionEnumeratedSets([Family('x'), NonNegativeIntegers()])
> in
> >FiniteSets()
> >False
> >
> >
> Nice! I hadn't seen that. I do think however that the check in
> CombinatorialFreeModule should be changed or at least that taking the
> disjoint union should print a warning that that this set is considered to
> be finite.
>
> Best,
>
> R.
>
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