code: public void connect(Node<T> o, Node<T> t) {
      if (!o.equals(t)) {
        o.connectTo(t);
        t.connectTo(o);
      }
    }
docs: Adds an edge between two given nodes, which must both belong to this graph. (Does nothing if the nodes are already connected)
  @param o the first given node
  @param t the second given node