https://www.chessprogramming.org/Mac_Hack
Mac Hack VI incorporated a table of opening positions with selected replies. The opening book was compiled by two MIT students, Larry Kaufman, a chess master and top rated U. S. Junior player, and Alan Baisley a chess expert. It is noteworthy that Larry Kaufman started his computer chess career over 50 years ago as team member of Mac Hack! Quote from Oral History of Richard Greenblatt:
And it was compacted pretty efficiently. And you know, there was a – by later standards it wasn't so big, but at the time it was pretty good sized. I don't know I think it was probably 8,000 or 10,000 moves in there. He – Kaufman spent quite a while doing it. Of course, a number of the moves, you know, would – the game would just play it. There was very little chance of it actually staying in the book. You know, the – but I think Kaufman did a good job and he did – we did perceive some of the – well of course, one of the basic things about computer programs, really to the present day, is that they're very tactical. It's much easier for them to see that the tactics than the strategy. So what's called a closed position is hard for a computer. That's where all the pieces are blocking each other and it's very long maneuvering. Whereas, an open position which is sort of tactical combinations is much more to the computer's liking. So therefore, when designing the opening book, you want to kind of play offbeat and kind of unbalanced type openings that tend to lead to these closed position – open positions, which are then good for the computer. And so we realized that and you know, I think Kaufman did a fairly good job of ...