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Draw a ring composed of tetrahedra connected at the edges that twists
and rotates toroidally.
When a series of tetrahedra are joined at the edges in a loop, it is
possible for them to rotate continously through the center without
deforming. This only works with an even number of tetrahedra, and
there must be eight or more, or they don't fit.
Written by Jamie Zawinski; 2013.