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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 iter_singleton_referents(self):
 """ Iterator of all of the singleton members of the context set. NOTE: this evaluates entities one-at-a-time, and does not handle relational constraints. """

        try:
            for member in self.__dict__['referential_domain'].iter_entities():
                if self['target'].is_entailed_by(member) and (self['distractor'].empty() or not self['distractor'].is_entailed_by(member)):
                    yield member['num'], member
        except KeyError:
            raise Exception("No referential_domain defined")