ABSTRACT
But is it true that there are two types of fold? Maybe there’s only one; the mountain fold can be turned into a valley fold merely by turning the paper over.
On the other hand, perhaps there are three types of fold: valley folds, mountain folds, and unfolds. If we fold the paper in half and unfold it, we will be left with a line on the papera crease-which is also a type of fold. Creases are sometimes merely artifacts, leftover marks from the early stages of folding, but they can also be useful tools. Creases can provide reference points (“fold this point to that crease”) and in the purest style of folding (no measuring devices, such as rulers, allowed) creases, folded edges, and their intersections are the only things that can serve as reference points. Creases are also commonly made in preparation for a complex maneuver.
