An optimization problem that appears as an exercise in most modern calculus textbooks is the crease length problem. Here, Ellermeyer provides a solution of the general crease length problem in which all possible foldings of a corner to the opposite edge are taken into account. One of his findings will be that the minimum crease length is never produced by a Case 2 fold and hence that the general crease length problem always yields a different minimum than the constrained problem that is treated in the textbooks. He discovers a criterion that determines which foldings must be performed in order to achieve the minimum (and maximum) crease lengths.
Ellermeyer, S.. (2008). A Closer Look at the Crease Length Problem. Mathematics Magazine, 81(2), 138-145.