*
 * <h3>Cancelling</h3>
 *
 * Any step in a pipeline can be {@linkplain #cancel(boolean) cancelled}, even after another step
 * has been derived, with the same semantics as cancelling a {@link Future}. In addition, a
 * successfully cancelled step will immediately start closing all objects captured for later closing
 * by it and by its input steps.
 *
 * <h3>Ending a pipeline</h3>
 *