@abstractmethod<EOL><INDENT>def is_adversarial(self, predictions, label):<DEDENT>
raise NotImplementedError<EOL>
Decides if predictions for an image are adversarial given
        a reference label.

        Parameters
        ----------
        predictions : :class:`numpy.ndarray`
            A vector with the pre-softmax predictions for some image.
        label : int
            The label of the unperturbed reference image.

        Returns
        -------
        bool
            True if an image with the given predictions is an adversarial
            example when the ground-truth class is given by label, False
            otherwise.