'Property method which returns the interior of a set.
The interior of a set S consists all points of S that do not
belong to the boundary of S.
Examples
>>> from sympy import Interval
>>> Interval(0, 1).interior
Interval.open(0, 1)
>>> Interval(0, 1).boundary.interior
EmptySet()'

@property
def interior(self):

    return (self - self.boundary)
