1. S. V. Manakov, Funktsion. Analiz Prilozh. 10 (4), 93 (1976).
2. A. P. Veselov, Dokl. Akad. Nauk 270 (6), 1298 (1983).
3. O. I. Bogoyavlenskii, Dokl. Akad. Nauk 287 (5), 1105 (1986).
4. M. V. Shamolin, Math. Models Comput. Simul. 7 (4), 389 (2015).
5. M. V. Shamolin, in Overall Results of Science and Technology. Thematical Reviews (VINITI, Moscow, 2013), Vol. 125, pp. 5–254 [in Russian].