I returned to this puzzle years later and had a revelation! Wahoo!

If anyone else is stuck towards the end of this puzzle and is getting a symbol that doesn't make sense, I offer a clarification on one of the letters: The fourth letter in the second row is a capital I (9th letter of the alphabet), not a lowercase l (12th letter of the alphabet). Good luck! And when will there be a third volume!!!

The master theorem - learning a new word every day!