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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 is_valid_mpls_label(label):
 """Validates `label` according to MPLS label rules RFC says: This 20-bit field. A value of 0 represents the "IPv4 Explicit NULL Label". A value of 1 represents the "Router Alert Label". A value of 2 represents the "IPv6 Explicit NULL Label". A value of 3 represents the "Implicit NULL Label". Values 4-15 are reserved. """

    if (not isinstance(label, numbers.Integral) or
            (4 <= label <= 15) or
            (label < 0 or label > 2 ** 20)):
        return False

    return True