def delta_set(x_prime, m):
    """
    Returns the set of all the ordered pairs having an input x-or equal
    to x_prime. It is the set of the ordered pairs (x, x_prime + x) modulo 2.
    m is the number of elements of the substitution box.
    """
    delta = set()
    for x in range(m):
        delta.add((x, x ^ x_prime))

    return delta