sclass StringTree2<A> {
  A leafValue;
  HashMap<S, StringTree2<A>> children = new HashMap;

  StringTree2<A> get(S s) {
    ret children.get(s);
  }
  
  StringTree2<A> getOrAdd(S s) {
    StringTree2<A> t = children.get(s);
    if (t == null)
      children.put(s, t = new StringTree2);
    ret t;
  }
}