It was closed-book. Take-home, closed-book seems like an oxymoron anyway. A lot of the cheating students would have concluded that other students are going to

It was closed-book. Take-home, closed-book seems like an oxymoron anyway. A lot of the cheating students would have concluded that other students are going to cheat and get a much better result, so they might as well do the same. The fault lies squarely with the professor.