code: def find_event_parent_with_event_child(self, parent_name, 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))
docs: 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.