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>:
> 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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