* </p>
     *
     * @param disposable
     *            A disposable resource. Must not be {@literal null}.
     */
    public static synchronized void addFirst(final Disposable disposable) {
        assertArgumentNotNull("disposable", disposable);
        disposables.addFirst(disposable);
    }

    /**
     * Unregisters a disposable resource.
     *
     * @param disposable

    abstract @Nullable N visitNext(Deque<Iterator<? extends N>> horizon);
  }

  /** Poor man's method reference for {@code Deque::addFirst} and {@code Deque::addLast}. */
  private enum InsertionOrder {
    FRONT {
      @Override
      <T> void insertInto(Deque<T> deque, T value) {
        deque.addFirst(value);
      }
    },
    BACK {
      @Override
      <T> void insertInto(Deque<T> deque, T value) {

        }
    }

    /**
     * Initializes the {@link Logger}.
     */
    protected static synchronized void initialize() {
        DisposableUtil.addFirst(() -> {
            initialized = false;
            loggers.clear();
            factory.releaseAll();
        });
        initialized = true;
    }

    /**