<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def DeregisterHelper(cls, helper_class):
 """Deregisters a helper class. The helper classes are identified based on their lower case name. Args: helper_class (type):
 class object of the argument helper. Raises: KeyError: if helper class is not set for the corresponding name. """

    helper_name = helper_class.NAME.lower()
    if helper_name not in cls._helper_classes:
      raise KeyError('Helper class not set for name: {0:s}.'.format(
          helper_class.NAME))

    del cls._helper_classes[helper_name]