when "Allow guests" is set, only the first guest can enter the lesson. The next one is told he has already taken the lesson

when "Student can retake" and "Allow guests" are set , every guest is considered to be the same person, so that when a particular guest hasn't completed the lesson before leaving, the next guest is asked if he would like to continue where he left off last time or start over

when "Student can retake" and "Allow guests" are set and "Unseen question in a cluster" is used, there comes a time when no more unseen questions are left after other guests have viewed them