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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_mac(mac):
 """Returns True if the given MAC address is valid. The given MAC address should be a colon hexadecimal notation string. Samples: - valid address: aa:bb:cc:dd:ee:ff, 11:22:33:44:55:66 - invalid address: aa:bb:cc:dd, 11-22-33-44-55-66, etc. """

    return bool(re.match(r'^' + r'[\:\-]'.join([r'([0-9a-f]{2})'] * 6)
                         + r'$', mac.lower()))