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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 GetMACBRepresentationFromDescriptions(self, timestamp_descriptions):
 """Determines the MACB representation from the timestamp descriptions. MACB representation is a shorthand for representing one or more of modification, access, change, birth timestamp descriptions as the letters "MACB" or a "." if the corresponding timestamp is not set. Note that this is an output format shorthand and does not guarantee that the timestamps represent the same occurrence. Args: timestamp_descriptions (list[str]):
 timestamp descriptions, which are defined in definitions.TIME_DESCRIPTIONS. Returns: str: MACB representation. """

    macb_representation = []

    if ('mtime' in timestamp_descriptions or
        definitions.TIME_DESCRIPTION_MODIFICATION in timestamp_descriptions):
      macb_representation.append('M')
    else:
      macb_representation.append('.')

    if ('atime' in timestamp_descriptions or
        definitions.TIME_DESCRIPTION_LAST_ACCESS in timestamp_descriptions):
      macb_representation.append('A')
    else:
      macb_representation.append('.')

    if ('ctime' in timestamp_descriptions or
        definitions.TIME_DESCRIPTION_CHANGE in timestamp_descriptions):
      macb_representation.append('C')
    else:
      macb_representation.append('.')

    if ('crtime' in timestamp_descriptions or
        definitions.TIME_DESCRIPTION_CREATION in timestamp_descriptions):
      macb_representation.append('B')
    else:
      macb_representation.append('.')

    return ''.join(macb_representation)