def gt_support(A,x):
    """
    Return set of support for probability vector x.
    Here A and x have the same length.  
    A is the list of candidates.
    x is a list of their probabilities.
    Probability is `non-zero' if it is greater than epsilon = 1e-6.
    """
    epsilon = 1e-6
    support = [ ]
    for (xi,a) in zip(x,A):
        if xi >= epsilon:
            support.append(a)
    return support