Finds all the immoralities in the model
        A v-structure X -> Z <- Y is an immorality if there is no direct edge between X and Y .

        Returns
        -------
        set: A set of all the immoralities in the model

        Examples
        ---------
        >>> from pgmpy.base import DAG
        >>> student = DAG()
        >>> student.add_edges_from([('diff', 'grade'), ('intel', 'grade'),
        ...                         ('intel', 'SAT'), ('grade', 'letter')])
        >>> student.get_immoralities()
        {('diff','intel')}

def get_immoralities(self):
        """
        Finds all the immoralities in the model
        A v-structure X -> Z <- Y is an immorality if there is no direct edge between X and Y .

        Returns
        -------
        set: A set of all the immoralities in the model

        Examples
        ---------
        >>> from pgmpy.base import DAG
        >>> student = DAG()
        >>> student.add_edges_from([('diff', 'grade'), ('intel', 'grade'),
        ...                         ('intel', 'SAT'), ('grade', 'letter')])
        >>> student.get_immoralities()
        {('diff','intel')}
        """
        immoralities = set()
        for node in self.nodes():
            for parents in itertools.combinations(self.predecessors(node), 2):
                if not self.has_edge(parents[0], parents[1]) and not self.has_edge(parents[1], parents[0]):
                    immoralities.add(tuple(sorted(parents)))
        return immoralities