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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 setdocument(self, doc):
 """Associate a document with this element. Arguments: doc (:class:`Document`):
 A document Each element must be associated with a FoLiA document. """

        assert isinstance(doc, Document)

        if not self.doc:
            self.doc = doc
            if self.id:
                if self.id in doc:
                    raise DuplicateIDError(self.id)
                else:
                    self.doc.index[id] = self

        for e in self: #recursive for all children
            if isinstance(e,AbstractElement): e.setdocument(doc)