1. Neĭmark, Yu. I. and Shil’nikov, L.P., Application of the Small-Parameter Method to a System of Differential Equations with Discontinuous Right-Hand Sides, Izv. Akad. Nauk SSSR, 1959, no. 6, pp. 51–59 (Russian).
2. Shil’nikov, L.P., Some Cases of Generation of Period Motions from Singular Trajectories, Mat. Sb. (N. S.), 1963, vol. 61(103), no. 4, pp. 443–466 (Russian).
3. Shil’nikov, L.P., A Case of the Existence of a Countable Number of Periodic Motions, Soviet Math. Dokl., 1965, vol. 6, pp. 163–166; see also: Dokl. Akad. Nauk SSSR, 1965, vol. 169, no. 3, pp. 558–561.
4. Shilnikov, L.P., On the Generation of a Periodic Motion from a TrajectoryWhich Leaves and Re-Enters a Saddle-Saddle State of Equilibrium, Soviet Math. Dokl., 1966, vol. 7, pp. 1155–1158; see also: Dokl. Akad. Nauk SSSR, 1966, vol. 170, no. 1, pp. 49–52.
5. Neimark, Yu. I. and Shil’nikov, L.P., A Case of Generation of Periodic Motions, Soviet Radiophys., 1965, vol. 8, pp. 234–241; see also: Izv. VUZ. Radiofizika, 1965, vol. 8, no. 2, pp. 330–340.