#18263: reintroduce `__neg__` for magmas cartesian product
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Reporter: vdelecroix | Owner:
Type: defect | Status: new
Priority: major | Milestone: sage-6.7
Component: categories | Resolution:
Keywords: | Merged in:
Authors: | Reviewers:
Report Upstream: N/A | Work issues:
Branch: | Commit:
Dependencies: #16836 | Stopgaps:
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Description changed by vdelecroix:
Old description:
> In #16836 the `__neg__` operation for cartesian product was moved from
> `AdditiveMagmas` to the `AdditiveMagmas.WithInverse()`. The operation was
> ambiguous but the feature is lost. It should be decided in this ticket
> what should be done with it.
>
> One should also restore the `TODO` section about `NN` being lazily import
> (or fix it ;-)
New description:
In #16836 the `__neg__` operation for cartesian product was moved from
`AdditiveMagmas` to the `AdditiveMagmas.WithInverse()`. The operation was
ambiguous but the feature is lost. We just revert the removal.
Moreover, there was a bug in Cartesian products of
`CombinatorialFreeModule` as this generic `__neg__` was called instead of
the customized `_neg_` which worked (see
[http://trac.sagemath.org/ticket/16836#comment:22 #16836 comment:22] and
[http://trac.sagemath.org/ticket/16836#comment:23 #16836 comment:23])! One
solution is to use `__neg__` everywhere instead of `_neg_`.
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Ticket URL: <http://trac.sagemath.org/ticket/18263#comment:1>
Sage <http://www.sagemath.org>
Sage: Creating a Viable Open Source Alternative to Magma, Maple, Mathematica,
and MATLAB
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