I’ve just run through Game 4 of Lesson 29: The Mastery Challenge, and this is the first one that’s really tripped me up. I’ve been able to get the correct solutions for all the games up to this point, though admittedly going way over time (like, 20 minutes per game rather than 7-9 minutes…drilling LGs for the next three weeks will hopefully get me test-ready come December, though!). Anyway, when I did Game 4, I made it into, basically, a double-layered sequencing game. In other words, I left open the possibility that more than one professor could be hired in any one year (though only under certain conditions; so, M and O still couldn’t be hired in the same year or in consecutive years, for instance, per the rules). It’s obviously much easier and makes a lot more sense the way that you solved it in the Trainer, but how/why did you make this inference, and how did you know it was permitted, given what the question stem says?
Nevermind, figured it out. Hindsight is 20/20!
Thank you again for your help and for saving me with your Trainer!