Gordian Knot 3D Puzzle

A friend who is into puzzles pointed me at this 3D puzzle http://www.cs.tau.ac.il/~efif/applications/puzzles/knot/ so I whipped it up in a few minutes in OpenSCAD.

If you get stuck, there is an animation showing the solution at http://www.youtube.com/watch?v=xNtNQRTdxps