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Comment by ammon | Hacker News Reader

I want to add that opening books are not THAT effective in computer chess either. Yes, they are significantly more effective than in computer go (because of the smaller branching factor and greater role of tactics). However, exponential increase in game tree size is crazy, even in chess. Thus, opening books really can't take you THAT far into a chess game (10 moves). An engine with a worse book but better search/eval will usually win.

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The main purpose of opening books is to beat any player who is strictly relying upon Stockfish (or LeelaZero's) output to play the game. Because these engines play very deterministically, you can beat people who just play's Stockfish #1 (or LeelaZero #1) move over and over.

I think the main issue with your initial statement was that you said you could beat someone just taking AlphaGo's advice on every move. Usually when people talk about opening books, they think of the opening book as being part of the engine's decision making process, not an addition to it. Usually this is literally the case, as in chess where I can add an opening book to Stockfish's runtime options.

In my opinion, it's really strange to describe this as an expert "beating" AlphaGo, when really it's just a technique for making AlphaGo stronger than it is without a huge pre-calculated cache of moves.

I've heard that opening books make Stockfish about 70 Elo better, which is very significant.

10 moves into a chess game is actually pretty far. The directions the game can go are massively narrowed 10 moves in.

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