code: def full_subgraph(self, vertices):
          
          obj_map = {vertex.id: vertex for vertex in vertices}
          edges = [
              edge for vertex_id in obj_map
              for edge in self._out_edges[vertex_id]
              if edge.head in obj_map
          ]
  
          return AnnotatedGraph(
              vertices=obj_map.values(),
              edges=edges,
          )
docs: Return the subgraph of this graph whose vertices
          are the given ones and whose edges are the edges
          of the original graph between those vertices.