#19016: Better hash for Element
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Reporter: | Owner:
ncohen | Status: needs_work
Type: | Milestone: sage-6.9
defect | Resolution:
Priority: | Merged in:
blocker | Reviewers:
Component: misc | Work issues:
Keywords: | Commit:
Authors: | 754dc5794a1a7004c8844cf7cfb64220957c36a5
Nathann Cohen | Stopgaps:
Report Upstream: N/A |
Branch: |
u/ncohen/19016 |
Dependencies: |
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Comment (by nbruin):
Replying to [comment:35 vdelecroix]:
> In other words, any (additive or multiplicative) magma element should be
immutable or adopt an mutable/immutable framework... might be a lot of
work to fix!
No, worse: any magma should have a decidable equality notion and a hash
that's compatible with it. As we've already seen, the mathematical notion
of equality in a magma need not be decidable. It makes no sense having a
hash if you cannot test equality.
I think the proper solution is to lose this equality and hashing
requirement and instead subclass to `MagmaWithDecidableEquality` and put
the hash & equality stuff there (or do it via categories/axioms if you
think that's more appropriate, but I'd rather avoid that if at all
possible).
Is that attainable? Another possibility is to by default only test
equality in the free structure covering the magma, i.e., "presentation
equality". But that's going to be very confusing.
--
Ticket URL: <http://trac.sagemath.org/ticket/19016#comment:37>
Sage <http://www.sagemath.org>
Sage: Creating a Viable Open Source Alternative to Magma, Maple, Mathematica,
and MATLAB
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