@Override
  public boolean add(@NotNull T t) {
    QueueEntry<T> newLast = new QueueEntry<>(t);
    boolean added = set.add(newLast);
    if (!added) return false;
    QueueEntry<T> oldLast = TOMB.prev;

    oldLast.next = newLast;
    newLast.prev = oldLast;
    newLast.next = TOMB;
    TOMB.prev = newLast;

    return true;
  }
@Override
  public boolean add(@NotNull T t)