sclass BetterLinkedHashSet<A> extends AbstractSet<A> {
  Map<A, Entry<A>> entries = hashMap();
  Entry<A> head, tail;
  
  sclass Entry<A> {
    A value;
    Entry<A> prev, next;
  }
  
  public bool add(A a) {
    if (entries.containsKey(a)) false;
    new Entry<A> n;
    n.value = a;
    n.prev = tail;
    if (tail != null) tail.next = n;
    tail = n;
    entries.put(a, n);
  }
  
  public bool remove(A a) {
    ret remove(entries.get(a));
  }
  
  public bool remove(Entry<A> node) {
    if (node == null) false;
    if (node.next != null) node.next.prev = node.prev; else tail = node.prev;
    if (node.prev != null) node.prev.next = node.next;
    entries.remove(node.value);
    true;
  }
}