code: func AsVertexList(s *Set) []Vertex {
  	rawList := s.List()
  	vertexList := make([]Vertex, len(rawList))
  	for i, raw := range rawList {
  		vertexList[i] = raw.(Vertex)
  	}
  	return vertexList
  }
docs: // simple convenience helper for converting a dag.Set to a []Vertex