Mobius strips are easy to make. Just glue one end of a strip of paper to the back side of the other end. Then you have a twisted strip. Lots of knitters make Mobius cowls as well. It’s a popular and cozy style. The author of some of the books I’ve used with students, mathematician Richard Evan Schwartz at Brown University, has been puzzling over a problem posed in the 1970s: what’s the shortest strip of paper you can use to make a Mobius strip? After a few years of tinkering, Dr. Schwartz cracked the problem. The key to doing…