Acknowledgments

We would like to thank David Bindel, Victor Ivrii, and Per-Olof Persson for their generous advice about MATLAB and the home page and movie set-ups.

The following sources of funding are also gratefully acknowledged: J.H. was supported in part by a Sloan fellowship and the NSF grant DMS-0901582, G.P’s visit to Berkeley in November of 2008 was supported in part by the France-Berkeley Fund, and M.Z. was supported in part by the NSF grant DMS-0654436.