}

    @SuppressWarnings("unchecked") // proxy for a generic class
    <V1, V2, V3, U> ClosingFunction3<V1, V2, V3, U> waitFor(
        ClosingFunction3<V1, V2, V3, U> closingFunction3) {
      return waitFor(closingFunction3, ClosingFunction3.class);
    }

    @SuppressWarnings("unchecked") // proxy for a generic class

     * @param <V2> the type returned by the second future
     * @param <V3> the type returned by the third future
     * @param <U> the type returned by the function
     */
    public interface ClosingFunction3<
        V1 extends @Nullable Object,
        V2 extends @Nullable Object,
        V3 extends @Nullable Object,
        U extends @Nullable Object> {
      /**

     * @param <V3> the type returned by the third future
     * @param <U> the type returned by the function
     */
    @FunctionalInterface
    public interface ClosingFunction3<
        V1 extends @Nullable Object,
        V2 extends @Nullable Object,
        V3 extends @Nullable Object,
        U extends @Nullable Object> {
      /**