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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 _remove_refs(self, keys):
 """Removes all references to all entries in keys. This does not cascade! :param Iterable[_ReferenceKey] keys: The keys to remove. """

        # remove direct refs
        for key in keys:
            del self.relations[key]
        # then remove all entries from each child
        for cached in self.relations.values():
            cached.release_references(keys)