@staticmethod
def _get_anchor_negative_triplet_mask(labels):
    """Return a 2D mask where mask[a, n] is True iff a and n have distinct labels.
        Args:
            labels: tf.int32 `Tensor` with shape [batch_size]
        Returns:
            mask: tf.bool `Tensor` with shape [batch_size, batch_size]
        """
    return ~(labels.unsqueeze(0) == labels.unsqueeze(1))
