def get_extra_imts(self, imts):
        """
        Returns the extra IMTs in the risk functions, i.e. the ones not in
        the `imts` set (the set of IMTs for which there is hazard).
        """
        extra_imts = set()
        for taxonomy in self.taxonomies:
            for (lt, kind), rf in self[taxonomy].risk_functions.items():
                if rf.imt not in imts:
                    extra_imts.add(rf.imt)
        return extra_imts
Returns the extra IMTs in the risk functions, i.e. the ones not in
        the `imts` set (the set of IMTs for which there is hazard).