Come again? When I search for "Yang-Mills" I get this:
http://en.wikipedia.org/wiki/Yang-Mills which does not seem overly related (maybe I'm stupid, but what does quantum chromodynamics have to do with either music or counting problems...!?). For "Mass gap" I get
http://en.wikipedia.org/wiki/Mass_gap and have the same question.
On a (presumably related??) note, I might as well yell: "SAT problem; let a solver construct the BDD and count the number of possibilities", but I'm old-fashioned and figure puzzles should be solved with understanding, not throwing overpowered tools at them and getting an answer which is correct, but which you don't understand.