If you are allowed to discuss assignments in a group, use the following rule. If you work out problems on a black or white board (or some other medium) with other students, do not copy the answer down from the board. Instead, go take a 30 minute sauna and then write up the answer on your own without the aid of work on the board. Copying work that is not yours is cheating, even if the work was done on the board as part of a discussion of a problem.