I was trying the some monotonicity testing functions such as the is_increasing function and it seems it is unable to return the solutions for some cases.

In [24]: expr = x - 1/x**2

In [25]: is_increasing(expr) # returns none 

it seems it stems from the following lines

as the following does not gives a solution, returns none

In [11]: og =  Interval.open(-oo,oo)

In [12]: sol = Union(Interval(-oo, -2**(1/3)), Interval.open(0, oo))

In [13]: og.is_subset(sol) # returns none should be false