def find_event_parent_with_event_child(self, parent_name, child_name):
        """Finds all event nodes (is_event node attribute is True) that are
        of the type parent_name, that have a child event node with the type
        child_name."""
        G = self.G
        matches = []
        for n in G.node.keys():
            if G.node[n]['is_event'] and G.node[n]['type'] == parent_name:
                children = G.successors(n)
                for child in children:
                    if G.node[child]['is_event'] and \
                            G.node[child]['type'] == child_name:
                        matches.append((n, child))
                        break
        return list(set(matches))