Late assignments will not be accepted, but your worst two or three problem sets will be dropped. You may find it pleasant and useful to work together on many portions of this course. I encourage you to do so. If you work together, do not work in a group that is too unbalanced. Certainly there are times when one person in a group has the key insight that solves a problem, but if the same person is always having all the insights, or if you are not contributing to the group effort, then you should probably seek out a different group.
Balance also extends to preparation.
Do not get answers or hints from someone who has completed the work before you have even begun. Ideally, each member of the group should come with roughly the same amount of background work done. Attendance I will not be recording attendance. Nevertheless, skipping class can have a detrimental effect on your grade in several ways. Most importantly, by missing class, you are missing an important part of the course.