Example of creating opening book from pgn file:
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Welcome to Critter Chess v0.40
By Richard Vida, Slovak Republic

Opening book file "book.cbk" not found

Hash table: 4194304 elements of 16 bytes = 64 MB total

makebook gm2001.pgn white.cbk whiteonly mingames 2 maxply 28 minscore 50

Input: "gm2001.pgn"   MaxPly: 28   MinGames: 2   MinScore: 50
Processing... 162248 entries from 33274 games
->white.cbk [19939 positions, 23843 entries, 381488 bytes total]

makebook gm2001.pgn black.cbk blackonly mingames 2 maxply 28 minscore 40

Input: "gm2001.pgn"   MaxPly: 28   MinGames: 2   MinScore: 40
Processing... 176336 entries from 33274 games
->black.cbk [15767 positions, 17998 entries, 287968 bytes total]

mergebook white.cbk black.cbk book.cbk

"white.cbk" + "black.cbk" -> "book.cbk"

Opening book: "white.cbk" - 23843 entries
Opening book: "black.cbk" - 17998 entries
... done
