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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 add_subkey(self, subkey):
 """ Add a new subkey to this key. Parameters subkey : AdfKey A new subkey. Notes ----- Duplicate check will not be performed if this is an 'Atoms' block. """

        if self.key.lower() == 'atoms' or not self.has_subkey(subkey):
            self.subkeys.append(subkey)