Khoma, N. H., and L. G. Khoma. “Generalized Periodic Solutions of Quasilinear Equations”.
Ukrains’kyi Matematychnyi Zhurnal
, vol. 48, no. 3, Mar. 1996, pp. 406-11,
https://umj.imath.kiev.ua/index.php/umj/article/view/5337
.