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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 is_restricted(self, assets, dt):
 """ An asset is restricted for all dts if it is in the static list. """

        if isinstance(assets, Asset):
            return assets in self._restricted_set
        return pd.Series(
            index=pd.Index(assets),
            data=vectorized_is_element(assets, self._restricted_set)
        )