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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 DeregisterDefinition(self, data_type_definition):
 """Deregisters a data type definition. The data type definitions are identified based on their lower case name. Args: data_type_definition (DataTypeDefinition):
 data type definition. Raises: KeyError: if a data type definition is not set for the corresponding name. """

    name = data_type_definition.name.lower()
    if name not in self._definitions:
      raise KeyError('Definition not set for name: {0:s}.'.format(
          data_type_definition.name))

    del self._definitions[name]