Advanced Backgammon Volume 2 by Bill Robertie - This is a perfect stepping stone for the intermediate/expert player looking to strengthen their game. This also doesn’t suffer from the poor formatting of Robertie’s 501. Again, some of the problems disagree with today’s bots, but that’s to be expected. What I personally enjoy is reading a book about a game I’m learning, backgammon here for example, getting better, rereading it, and taking note of problems/positions that I thought another play may be called for. With GNU backgammon everyone has free access to a top level robot to analyze positions for them, so you can simply put the position in and find out who is right, and hopefully learn something in the process. I found that this series helped advance my game more than his 501 Essential BG Problems. There are also some glaring errors such as Robertie stating the wrong person on roll, or one side having too many checkers, somewhere in Robertie’s books there was an easily countable pip count that was off by 10 pips, etc…