#19040: rewrite Expression.__nonzero__()
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Reporter: rws | Owner:
Type: enhancement | Status: needs_info
Priority: major | Milestone: sage-6.9
Component: symbolics | Resolution:
Keywords: | Merged in:
Authors: | Reviewers:
Report Upstream: N/A | Work issues:
Branch: | Commit:
Dependencies: | Stopgaps:
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Comment (by vdelecroix):
Replying to [comment:43 rws]:
> Replying to [comment:41 vdelecroix]:
> > What would be the difference between the output `NotImplemented` and
`Undecidable`!?
> >
> > As I already mentioned in [comment:24 comment 24], it makes few sense
that `satisfiable(expr)` returns `Undecidable`. Each formula is either
`True` or `False`. I am here only assuming that mathematics are
consistent. Of course `satisfiable` can not work for all input and when it
can not it should return `NotImplemented`. That being said, some formula
`expr` have no proof of their truthness (from Godel), but then I doubt any
computer would actually be able to prove it.
> Agreed if we look at equalities. Inequalities can be undecidable if we
know one side has no order relation. I don't know if there could be other
reasons. I haven't decided yet if `__nonzero__` should throw an exception
for this.
What do you mean? Do you have an example of such inequality.
> >`for all x, exists y, for all z expr(x,y,z)`
> Such will not be in the first versions.
But do you have a syntax in mind for it. It would be cool to not multiply
ad libitum the `satisfiable`, `holds`, etc which are exactly the same
thing with a choice of quantifiers.
--
Ticket URL: <http://trac.sagemath.org/ticket/19040#comment:44>
Sage <http://www.sagemath.org>
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