(self)
Return the class used to construt the dual.
Return the class used to construt the dual.
Return the class used to construt the dual .
def dual_class(self):
        """Return the class used to construt the dual."""
        raise NotImplementedError(
            'dual_class must be implemented in a subclass'
        )
def dual_class ( self ) : raise NotImplementedError ( 'dual_class must be implemented in a subclass' )