Hofer, H., K. Wysocki, and E. Zehnder. “Unknotted Periodic Orbits for Reeb Flows on the Three-Sphere”. Topological Methods in Nonlinear Analysis 7, no. 2 (June 1, 1996): 219–244. Accessed July 22, 2024. https://apcz.umk.pl/TMNA/article/view/TMNA.1996.010.