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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 find_shadowed(self, extra=()):
 """Find all the shadowed names. extra is an iterable of variables that may be defined with `add_special` which may occour scoped. """

        i = self.identifiers
        return (i.declared | i.outer_undeclared) & \
               (i.declared_locally | i.declared_parameter) | \
               set(x for x in extra if i.is_declared(x))