Print out the html page on Arrow's impossibility theorem from the online notes. Annotate the entire set of slides before class by writing questions, writing your notes, and making clarifications. Bring a copy of the annotated notes to class and turn it in at the start of the class. Most students like to have their annotated proof in front of them for the lecture, so it is probably best to photocopy your annotated proof and turn in the photocopy.