Disclosure: The applet below is merely an illustration. We do not prove that everything is well-defined.

Note 1: You can turn off the spaces (around "intersections" of strands) if you like. The spaces were designed for color blind people. We want them to be able to see which strand is on top of which.

Note 2: Click on the "Start animation" button to start animation whenever the button is enabled (which is almost always). If the "Start animation" button is disabled, click "Next" to see the next slide.