This construction shows Villarceau circles[1], which are the nontrivial circle sections of a torus. This can be also seen on the POV raytracer hall of fame[2].

This construction shows Villarceau circles[1], which are the nontrivial circle sections of a torus. This can be also seen on the POV raytracer hall of fame[2]. [1]: http://en.wikipedia.org/wiki/Villarceau_circles [2]: http://hof.povray.org/Villarceau_Circles-CSG.html