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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 visit_Set(self, node):
        '''
        A set is abstracted as an unordered container of its elements

        >>> from pythran import passmanager
        >>> pm = passmanager.PassManager('demo')
        >>> module = ast.parse('def foo(a, b): return {a, b}')
        >>> result = pm.gather(Aliases, module)
        >>> Aliases.dump(result, filter=ast.Set)
        {a, b} => ['|a|', '|b|']

        where the |id| notation means something that may contain ``id``.
        '''
        if node.elts:
            elts_aliases = {ContainerOf(alias)
                            for elt in node.elts
                            for alias in self.visit(elt)}
        else:
            elts_aliases = None
        return self.add(node, elts_aliases)