code: public String moreToString() {
          StringBuilder sb = new StringBuilder("Last cert?  ");
          sb.append((index == -1) ? "Yes" : "No");
          sb.append("\n");
          return sb.toString();
      }
docs: return Vertex index as String compatible with
  the way other Vertex.xToString() methods display
  information.
  
  @returns String form of index as "Last cert?  [Yes/No]