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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 promotePrefixes(self):
 """ Push prefix declarations up the tree as far as possible. Prefix mapping are pushed to its parent unless the parent has the prefix mapped to another URI or the parent has the prefix. This is propagated up the tree until the top is reached. @return: self @rtype: L{Element} """

        for c in self.children:
            c.promotePrefixes()
        if self.parent is None:
            return
        for p, u in self.nsprefixes.items():
            if p in self.parent.nsprefixes:
                pu = self.parent.nsprefixes[p]
                if pu == u:
                    del self.nsprefixes[p]
                continue
            if p != self.parent.prefix:
                self.parent.nsprefixes[p] = u
                del self.nsprefixes[p]
        return self