static class LinkedTreeMap<A, B> extends AbstractMap<A, B> {
  Map<A, B> map;
  new LinkedList<A> list;

  *() { map = new TreeMap; }
  *(Map<A, B> *map) {}

  public B get(Object key) {
    ret map.get(key);
  }
  
  public B put(A key, B value) {
    if (!map.containsKey(key))
      list.add(key);
    return map.put(key, value);
  }
  
  public bool containsKey(O key) {
    ret map.containsKey(key);
  }
  
  public Set<Map.Entry<A,B>> entrySet() {
    ret map.entrySet();
  }
}

Began life as a copy of #1018325