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?
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