#10963: More functorial constructions
-------------------------------------+-------------------------------------
Reporter: nthiery | Owner: stumpc5
Type: enhancement | Status: needs_info
Priority: major | Milestone: sage-6.2
Component: categories | Resolution:
Keywords: days54 | Merged in:
Authors: Nicolas M. Thiéry | Reviewers: Simon King, Frédéric
Report Upstream: N/A | Chapoton
Branch: | Work issues:
public/ticket/10963-doc- | Commit:
distributive | 3e2003ded77192465cc3e99fec7fa64dae998950
Dependencies: #11224, #8327, | Stopgaps:
#10193, #12895, #14516, #14722, |
#13589, #14471, #15069, #15094, |
#11688, #13394, #15150, #15506 |
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Comment (by nthiery):
Replying to [comment:494 pbruin]:
> Thanks for looking at it! There seems to be a typo (12963 instead of
10963 in various places). Didn't you run into problems with using
`deprecated_function_alias()` everywhere? I tried this first, but (if I
recall correctly) when running doctests there was a problem due to a
circular import, and another error caused by applying
`deprecated_function_alias()` to a `cached_method`.
Indeed! That's why I got distracted by #15757 and #15759. It itched me
not to be able to use deprecated_function_alias :-)
Thanks for spotting the 12963's. I'll fix them now.
> As for which of `summand_embedding()` and `cartesian_embedding()` in
`CombinatorialFreeModule` is the "real" one: you probably wanted to make
the definitions look more symmetrical, and of course it makes no practical
difference. Just to explain my motivation for doing it the other way
around than for `*_projection()`: for a direct sum it is the embeddings
that exist by definition, while for a Cartesian product is is the
projections. The fact that you do have a `cartesian_embedding()` in this
setting follows from a theorem (product = sum for modules), not a
definition, so it seemed more natural to regard `summand_embedding()` as
the "primary" notion.
Ah ah, that's an interesting motivation indeed! Thanks for sharing
it. I'll keep it in mind if this occurs elsewhere, in which case it
could well make much sense to introduce this subtlety.
Cheers,
Nicolas
--
Ticket URL: <http://trac.sagemath.org/ticket/10963#comment:496>
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