1. V. M. Miklyukov, A. A. Klyachin, and V. A. Klyachin,
http://www.uchimsya.info/maxsurf.pdf
.
2. V. N. Berestovskii and V. M. Gichev, St. Petersb. Math. J. 11 (4), 543–565 (2000).
3. M. Grochowski, J. Dyn. Control Syst. 12 (2), 145–160 (2006).
4. V. R. Krym and N. N. Petrov, Vestn. S.-Peterb. Univ., Ser. 1., No. 3, 68–80 (2008).
5. W. Craig and S. Weinstein, Proc. R. Soc. A 465 (2110), 3023–3046 (2008).