Graphviz 如何显示节点的相同标题

我想在维基上画RB树

但我找不到为不同节点显示相同标题的可能性（在本例中为nil-nodes）。有可能吗

  digraph "rb-tree"{
  bgcolor = whitesmoke;
  forcelabels = true;
  margin = 0;
  node [shape = circle,
        style = filled,
        fontsize = 14,
        margin = 0,
        fillcolor = black,
        fontcolor = white];
  edge [fontsize = 10,
        arrowhead = vee];
8 [fillcolor = red];
17 [fillcolor = red];
nil_8l [shape = box];
nil_8r [shape = box];
nil_17l [shape = box];
nil_17r [shape = box];
13->8;
13->17;
8->nil_8l;
8->nil_8r;
17->nil_17l;
17->nil_17r;
}

---

Graphiz可以设置标签。因此，请使用：

 digraph "rb-tree"{
  bgcolor = whitesmoke;
  forcelabels = true;
  margin = 0;
  node [shape = circle,
        style = filled,
        fontsize = 14,
        margin = 0,
        fillcolor = black,
        fontcolor = white];
  edge [fontsize = 10,
        arrowhead = vee];
8 [fillcolor = red];
17 [fillcolor = red];
nil_8l [shape = box label="nil"];
nil_8r [shape = box label="nil"];
nil_17l [shape = box label="nil"];
nil_17r [shape = box label="nil"];
13->8;
13->17;
8->nil_8l;
8->nil_8r;
17->nil_17l;
17->nil_17r;
}

---

这个问题很模糊。为落选做好准备。不是我说的，但是…欢迎来到Stack Overflow。请拿着这本书学习。然后，给我们一个清晰的描述，你想做什么，你错了什么，你期望得到什么，以及一个简单的答案。