I've been struggling through that lately. I keep getting distracted trying to prove or disprove there is a solution to the MU puzzle. He will present a new idea and I always have to go back and check to see if I can make any headway. I've tried the problem forwards, backwards, and from a numerical standpoint of counting I's. I just want to get to the end of the book and know whether or not it is possible.

Regardless, that book will make your brain fold in it's self. Highly recommended.