#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):
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.
In an ideal world, the function `satisfiable(expr)` would return one of:
- `(True, example)`
- `(False, proof)`
- `NotImplemented`
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Ticket URL: <http://trac.sagemath.org/ticket/19040#comment:41>
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