Odani, Kenzi: On the limit cycle of the van der Pol equation.
(English).
In:
Došlá, Z., Kuben, J.
and Vosmanský, J. (eds.): Proceedings of Equadiff 9, Conference on Differential Equations and Their Applications, Brno, August 25-29, 1997.
[Part 3] Papers.
Masaryk University, Brno, 1998.
pp. 229-235