user2736: I have seen some commentary that implies that Stockfish did not have access to an opening book in its much-reported match with AlphaZero, but I cannot find a conclusive citation, and my inability to do so has me wondering if maybe Stockfish did have an opening book after all.
For example:

GM Hikaru Nakamura...called the match "dishonest" and pointed out that
  Stockfish's methodology requires it to have an openings book for
  optimal performance. While he doesn't think the ultimate winner would
  have changed, Nakamura thought the size of the winning score would be
  mitigated.

or, from a StackExchange answer:

Stockfish...wasn't allowed to use an opening book which makes it
  consider many moves in shallow depths.

It's worth noting that even if Stockfish didn't have an opening book for the canonical 100 game match, page 6 of the paper shows that AlphaZero is dominant when you start from a variety of common openings. Nonetheless I wonder why they would handicap Stockfish this way.

user15296: Stockfish stopped using opening books a long time ago. That is, it's an engine, and if you want to use an opening book, you have to use it in UI that you use to play the game or in the software you use to interface with the engine, playing book moves without even telling Stockfish about that.
There's no way to tell Stockfish about existing books (the commands were removed completely), and it's not expecting to use any.
OTOH, Stockfish can and would gladly use end game tables (Syzygy).

user15223: To add to SmallChess's answer, Stockfish as an engine doesn't come with an opening book. Those are separate inputs, and you can give Stockfish whatever opening book you want. Therefore, if the AlphaZero paper doesn't say the authors gave Stockfish an opening book, it didn't have one.
See this thread on Chess.com for more about Stockfish playing with the Cerebellum opening book (aka "Brainfish"). You can see from the rating list that the opening book is worth about 50 elo - a substantial amount. You can also see the difference in the TCEC S14 superfinal, which was played with set openings, and the rapid bonus afterwards, played without books. Leela (an AlphaZero clone) narrowly lost the superfinal, but annihilated Stockfish in the bookless bonus.

user825: Both Nakamura and the StackExchange answer were correct - Stockfish didn't use an opening book. I think Google did that to make a fair comparison as AlphaZero wasn't using an opening book as well.
EDIT
I didn't see anything about opening book for Stockfish in the paper. I'm not the only one.

http://talkchess.com/forum/viewtopic.php?t=65910&postdays=0&postorder=asc&highlight=stockfish+book&topic_view=flat&start=10
As far as I read the paper, I didn't see a book for Stockfish mentioned, so I guess, match was bookless.

and

http://talkchess.com/forum/viewtopic.php?t=65909&highlight=stockfish+book
While this is indeed incredible, show me how it beats SF dev with good book and syzygy on equal hardware in a 1000 game match.


2736: <p>I have seen some commentary that implies that Stockfish did not have access to an opening book in its much-reported match with AlphaZero, but I cannot find a conclusive citation, and my inability to do so has me wondering if maybe Stockfish did have an opening book after all.</p>

<p><a href="https://www.chess.com/news/view/google-s-alphazero-destroys-stockfish-in-100-game-match" rel="noreferrer">For example</a>:</p>

<blockquote>
  <p>GM Hikaru Nakamura...called the match "dishonest" and pointed out that
  Stockfish's methodology requires it to have an openings book for
  optimal performance. While he doesn't think the ultimate winner would
  have changed, Nakamura thought the size of the winning score would be
  mitigated.</p>
</blockquote>

<p>or, from <a href="https://chess.stackexchange.com/a/19378/2736">a StackExchange answer</a>:</p>

<blockquote>
  <p>Stockfish...wasn't allowed to use an opening book which makes it
  consider many moves in shallow depths.</p>
</blockquote>

<p>It's worth noting that even if Stockfish didn't have an opening book for the canonical 100 game match, page 6 of <a href="https://arxiv.org/pdf/1712.01815.pdf" rel="noreferrer">the paper</a> shows that AlphaZero is dominant when you start from a variety of common openings. Nonetheless I wonder why they would handicap Stockfish this way.</p>
 15296: <p>Stockfish stopped using opening books a long time ago. That is, it's an engine, and if you want to use an opening book, you have to use it in UI that you use to play the game or in the software you use to interface with the engine, playing book moves without even telling Stockfish about that.</p>
<p>There's no way to tell Stockfish about existing books (the commands were removed completely), and it's not expecting to use any.</p>
<p>OTOH, Stockfish can and would gladly use end game tables (Syzygy).</p>
 15223: <p>To add to SmallChess's answer, Stockfish as an engine doesn't come with an opening book. Those are separate inputs, and you can give Stockfish whatever opening book you want. Therefore, if the AlphaZero paper doesn't say the authors gave Stockfish an opening book, it didn't have one.</p>

<p>See <a href="https://www.chess.com/forum/view/general/how-to-install-brainfish-the-best-chess-program-in-the-world" rel="nofollow noreferrer">this thread</a> on Chess.com for more about Stockfish playing with the Cerebellum opening book (aka "Brainfish"). You can see from the rating list that the opening book is worth about 50 elo - a substantial amount. You can also see the difference in the TCEC S14 superfinal, which was played with set openings, and the rapid bonus afterwards, played without books. Leela (an AlphaZero clone) narrowly lost the superfinal, but annihilated Stockfish in the bookless bonus.</p>
 825: <p>Both Nakamura and the StackExchange answer were correct - Stockfish didn't use an opening book. I think Google did that to make a fair comparison as AlphaZero wasn't using an opening book as well.</p>
<p><strong>EDIT</strong></p>
<p>I didn't see anything about opening book for Stockfish in the paper. I'm not the only one.</p>
<blockquote>
<p><a href="http://talkchess.com/forum/viewtopic.php?t=65910&amp;postdays=0&amp;postorder=asc&amp;highlight=stockfish+book&amp;topic_view=flat&amp;start=10" rel="noreferrer">http://talkchess.com/forum/viewtopic.php?t=65910&amp;postdays=0&amp;postorder=asc&amp;highlight=stockfish+book&amp;topic_view=flat&amp;start=10</a></p>
<p>As far as I read the paper, I didn't see a book for Stockfish mentioned, so I guess, match was bookless.</p>
</blockquote>
<p>and</p>
<blockquote>
<p><a href="http://talkchess.com/forum/viewtopic.php?t=65909&amp;highlight=stockfish+book" rel="noreferrer">http://talkchess.com/forum/viewtopic.php?t=65909&amp;highlight=stockfish+book</a></p>
<p>While this is indeed incredible, show me how it beats SF dev with good book and syzygy on equal hardware in a 1000 game match.</p>
</blockquote>
