'Returns True if \'self\' is a subset of \'other\'.
Examples
>>> from sympy import Interval
>>> Interval(0, 0.5).is_subset(Interval(0, 1))
True
>>> Interval(0, 1).is_subset(Interval(0, 1, left_open=True))
False'

def is_subset(self, other):

    if isinstance(other, Set):
        return (self.intersect(other) == self)
    else:
        raise ValueError(("Unknown    argument    '%s'" % other))
