#17142: Return type of some poset functions
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Reporter: jmantysalo | Owner:
Type: defect | Status: new
Priority: major | Milestone: sage-wishlist
Component: combinatorics | Resolution:
Keywords: | Merged in:
Authors: | Reviewers:
Report Upstream: N/A | Work issues:
Branch: | Commit:
Dependencies: | Stopgaps:
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Description changed by jmantysalo:
Old description:
> If `P` is a lattice -- not just a poset -- then also `P.dual()` returns
> lattice. But `P.product(P)` gives poset, not lattice. Also at least
> `product` forgots facade, i.e. if `P=Poset({0:[1]}, facade=False)`, then
> `P.Product(P)` has elements of type plain 'tuple'. `subposet()` seems to
> work.
>
> Functions should be checked one by one for this. This needs also some
> thinking: for example dual of meet-semilattice is join-semilattice.
New description:
If `P` is a lattice -- not just a poset -- then also `P.dual()` returns
lattice. But `P.product(P)` gives poset, not lattice. Also at least
`product` forgots facade, i.e. if `P=Poset({0:[1]}, facade=False)`, then
`P.Product(P)` has elements of type plain 'tuple'. `subposet()` seems to
work, `relabel` does not.
Functions should be checked one by one for this. This needs also some
thinking: for example dual of meet-semilattice is join-semilattice.
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Ticket URL: <http://trac.sagemath.org/ticket/17142#comment:1>
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