Capturing a convex polygonal object in the plane with three disc-shaped robots

• Suppose the polygonal object turns while maintaining simultaneous contact with two fixed robots. Then, the locus of an arbitrary vertex of the polygon is a Limacon of Pascal. Here is a Cinderella file powered by a Java applet that demonstrates this: quartic.html.
• The motion of the polygonal object can be discontinuous.
  [discontinuity.eps, discontinuity.fig
  discont.ps, discont.tex]