Copyright (c) 2000 by M. Mukhopadhyay. All rights reserved.
Definitions of mountain fold, valley fold and preliminary bases can be found in
Origami For Everyone.
It is possible to arrive at finished models that look the same
using other kinds of units. Also, if you valley crease diagonal ab of unit A, it can be assembled like sonobes. For assembly of 12 or more of such units to make other polyhedra please refer to books.