def Pf(lea1):
    """ returns the probability that given lea1 is True;
        the probability is expressed as a float between 0.0 and 1.0;
        raises an exception if the probability type is no convertible to float
        raises an exception if some value in the distribution is not boolean
        (note this is NOT the case with lea1.p(True));
        this is a convenience function equivalent to lea1.Pf
    """
    return lea1.Pf
