On this the White Rabbit blew three blasts on the trumpet, and
then unrolled the parchment scroll, and read as follows:--

    `The Queen of Hearts, she made some tarts,
          All on a summer day:
      The Knave of Hearts, he stole those tarts,
          And took them quite away!'

  `Consider your verdict,' the King said to the jury.

  `Not yet, not yet!' the Rabbit hastily interrupted.  `There's

  On this the White Rabbit blew three blasts on the trumpet, and
then unrolled the parchment scroll, and read as follows:--

    `The Queen of Hearts, she made some tarts,
          All on a summer day:
      The Knave of Hearts, he stole those tarts,
          And took them quite away!'

  `Consider your verdict,' the King said to the jury.

  `Not yet, not yet!' the Rabbit hastily interrupted.  `There's

 * is by declaring that step to be the last step of the pipeline. Nevertheless, we refer to the
 * "value" of a successful step or the "result" (value or exception) of any step.
 *
 * <ol>
 *   <li>A pipeline starts at its leaf step (or steps), which is created from either a callable
 *       block or a {@link ListenableFuture}.
 *   <li>Each other step is derived from one or more input steps. At each step, zero or more objects