sclass PerfectTokenList extends AbstractList<S> {
  LogNArray<Token> list = new LogNArray;
  new MultiMap<S, Token> index;
  
  sclass Token {
    Token prev, next;
    S text;
  }
  
  sS text(Token t) { ret t == null ? null : t.text; }
  
  public S get(int i) { ret text(list.get(i)); }
  public int size() { ret l(list); }
}