I learned last month that the "napkin problem" that I've attributed to Margulis (an attribution that seems to be widespread: see for instance www.ics.uci.edu/~eppstein/junkyard/napkin.html) was actually introduced by Vladimir Arnold. Or at least, this is what Arnold says; see page viii of the book "Arnold's Problems". So unless Margulis has claimed credit for the problem, we should all start attributing it to Arnold. This problem asks whether it is possible to fold a square napkin into a flat shape whose outline has larger perimeter than the original unfolded napkin. Serge Tabachnikov tells me that the problem has a positive solution if arbitrary origami-type folding is allowed (I'd seen this claimed before, and saw a preprint that purported to give the construction, but I never checked the details to see if I really believed it), and it has a negative solution if each successive fold is required to be of the form "Take the existing flat shape and fold it over a line that cuts all the way through it to obtain another flat shape". Serge did not provide me with citations, though, so if any of you can provide them, I'd be grateful. Jim Propp