'Compute the CDF from the PDF
Returns a Lambda'

@cacheit
def compute_cdf(self, **kwargs):

    (x, z) = symbols('x,    z', real=True, finite=True, cls=Dummy)
    left_bound = self.set.start
    pdf = self.pdf(x)
    cdf = integrate(pdf, (x, left_bound, z), **kwargs)
    cdf = Piecewise((cdf, (z >= left_bound)), (0, True))
    return Lambda(z, cdf)
