** Using WeBWorK **

Ah -- much easier, and probably a bit safer in that it's quicker to revert to the default "nobody" behavior.

As to comments that the best thing might be to give everybody credit: I'd like to do that, except that there were a number of students who did not even attempt this problem (and some who did not do the set at all). I have strong reservations about giving them credit. One reason is my past experience that students who do the work resent others getting credit who did not do the work; they consider this lack of fairness by the instructor.