docs: def add_outward_edge(self, v, e):
          """ Add an outward edge to a vertex
  
          :param v: The source vertex.
          :param e: The name of the outward edge.
          """
          self.add_vertex(v)
          self.graph.add_vertex(e)
          self.es.add(e)
          self.graph.add_edge(e, v)