Le mercredi 07 décembre 2011 à 20:36 +0100, krastanov.ste...@gmail.com a
écrit :
> How should assumptions be used? More precisely why the following code
> does what it does
>
> In [18]: global_assumptions.clear()
>
> In [19]: x = Symbol('x', positive=True)
>
> In [20]: ask(Q.positive(x)) # Why does it return None?
>
> In [21]: x > 0
> Out[21]: True
>
> In [22]: global_assumptions # It's empty but I already declared x as
> positive
> Out[22]: AssumptionsContext()
>
> In [23]: ask(Q.positive(x))
>
> In [24]: global_assumptions.add(Q.positive(x))
>
> In [25]: ask(Q.positive(x))
> Out[25]: True
>
> Why setting a symbol to positive does not create a global assumption?
> What are assumption used for actually when there are all the
> is_something flags?
The is_foo flags are part of the old assumption system, while ask() and
global_assumptions belong to the new one. The two systems ignore each
other and your session demonstrates precisely this.
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