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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 to_immutable(self):
 """Get an immutable version of this collection."""

        if self._enumeration is None:
            self._get_mutable_enumeration()
        col_obj = self._enumeration['immutable'][self._collection_type]
        return col_obj(self.header, self.values)