ABSTRACT
The conclusion is very simple. Iso-area folds should be regarded as posessing a kind of “rotational inverse symmetry”.
The combined operation of rotation by 360/n degrees (where n is a natural number) and inversion through the origin is called the “n-fold rotation inverse operation”. The sequence of rotation and inversion can be changed. When a figure (solid) is not changed by an n-fold rotation inverse operation, it is said to have “n-fold rotational inverse symmetry,” denoted by n-bar (or n, see Figure 2). I will use “n-bar symmetry” instead of “n-fold rotational inverse symmetry” in this paper, for brevity and clarity.
