Yes, I went way off in the wrong direction at first. There is a Fajr Cup chess tournament. "play fajr" so, 'play chess'... The last names "Welts" and "Weeks" show up fairly prominently in a chess search online. and, golly!, there's also a chess cipher, which it obviously wasn't, but I spent a fair amount of time looking in that direction. I am buffing my nails a little, though, by noting that I did spot the key right away. That's something, at least!

I felt a momentary annoyance with the typo which turned fair into fajr. I looked it up, though, and it turns out it's a thing! I'm going to look at it some more and see if I can cook up a way to apply it to solving the puzzle...

I figured the typo was intentional but I was way off at first. Don't google "fajr cipher", all the top hits are Al-Qaeda related. I might be on a list now. As someone who is new to ciphers I thought this one was a great challenge!

I think that the "play fair" part of the theorem suggests that the entire puzzle is a playfair cipher. (just got the book and think it's awesome btw)