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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def rank(idx, dim):
 """Calculate the index rank according to Bertran's notation."""

    idxm = multi_index(idx, dim)
    out = 0
    while idxm[-1:] == (0,):
        out += 1
        idxm = idxm[:-1]
    return out