'Return the union of intervals of `x` when, self is in
rectangular form, or the union of intervals of `r` when
self is in polar form.
Examples
>>> from sympy import Interval, ComplexRegion, Union
>>> a = Interval(2, 3)
>>> b = Interval(4, 5)
>>> c = Interval(1, 7)
>>> C1 = ComplexRegion(a*b)
>>> C1.a_interval
Interval(2, 3)
>>> C2 = ComplexRegion(Union(a*b, b*c))
>>> C2.a_interval
Union(Interval(2, 3), Interval(4, 5))'

@property
def a_interval(self):

    a_interval = []
    for element in self.psets:
        a_interval.append(element.args[0])
    a_interval = Union(*a_interval)
    return a_interval
