BJ Penn's book of MMA knowledge.

Brazilian Jujitsu Theory and Techniques by Royler Gracie.

Encyclopedia of Brazilian Jujitsu by Rigan Machado.

If I had to choose just one, I would probably go with the Encyclopedia of Brazilian Jujitsu, but they are all worth the money.
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"In case you ever wondered what it's like to be knocked out, it's like waking up from a nightmare only to discover it wasn't a dream." -Forrest Griffin