See BP851 for a version where the figure must stay within the 2D plane and cannot pass through itself while being deformed.
Adjacent-numbered pages: BP364 BP365 BP366 BP367 BP368  *  BP370 BP371 BP372 BP373 BP374
nice, math, traditional
zoom in left (figure_made_of_curves_and_quotient_by_hollow_dots)
Aaron David Fairbanks