On Thu, May 31, 2012 at 1:59 AM, [email protected]
<[email protected]> wrote:
> And another one:
>
> In [108]: solve([x**2+1], [x])
> Out[108]: []
>
> In [109]: solve([x**2+1], [y])
> returns None
>
> So when exactly is None returned and when exactly is an empty list
> returned? Assuming the input is solve(list, list)
None - there is no subset of symbols whose value can make the expression zero
[] - the symbols are valid -- in the free symbols -- but no values
gave solutions that satisfied the expr; in this case you must have x
as real since
```
>>> solve([x**2+1],[x])
[(-I,), (I,)]
```
In the canonical_solve these both get mapped to {} with the 'solve() or {}'
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