I am not sure, but I believe that this was probably changed in #14140
when SetPartition was changed from a CombinatorialClass to a
ClonableArray. It doesn't look like it changed in #15143 but additional
changes to the SetPartition class were made there.
It seems like the easiest fix would to write something like
a method `to_set_of_sets` or add directly the `intersection` method
in the element methods for SetPartition. Both might be useful
for other users.
-Mike
On Monday, 28 October 2013 11:54:41 UTC-4, Vincent Delecroix wrote:
>
> I forwarded your e-mail to sage-combinat as it might be of interest there.
>
> Isn't there a problem of Element (a set partition) which want at the
> same time to be a Parent here (ie a set) ?I guess it would be
> impossible to cleanly solve the issue in the actual state of the
> Parent/Element implementation...
>
> Vincent
>
> 2013/10/28, Rob Beezer <goo...@beezer.cotse.net <javascript:>>:
> > SetPartitions() used to create sets of sets (as of, say January 2013).
> > That seems to be broken as most common methods on sets will fail (but
> not
> > all). Any ideas on a simple fix or a good workaround (or an indication
> of
> > what I am doing wrong)? I can use the standard_form() method to get a
> list
> >
> > of lists, which I can convert back to sets of sets, but that is very
> > unnatural (and the reordering will mean lots of needless editing of a
> very
> > long string of doctests).
> >
> > Thanks in advance for any ideas. I can make a trac ticket if that is
> > called for.
> >
> > Rob
> >
> > sage: S = SetPartitions([1,2,3,4], [2,2]).list()
> > sage: S
> > [{{1, 2}, {3, 4}}, {{1, 3}, {2, 4}}, {{1, 4}, {2, 3}}]
> >
> > sage: S[0].cardinality()
> > 2
> >
> > sage: S[0].intersection(S[1])
> > AttributeError: 'SetPartitions_setparts_with_category.element_class'
> object
> >
> > has no attribute 'intersection'
> >
> > sage: Set(S[0])
> > TypeError: Element has no defined underlying set
> >
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