Samoilenko , A. M., and G. P. Pelyukh. 1991. “On Existence and Uniqueness of Solutions of the Sets of Nonlinear Differential-Difference Equations of Neutral Type Bounded on the Whole Axis”. Ukrains’kyi Matematychnyi Zhurnal 43 (3): 390-94. https://umj.imath.kiev.ua/index.php/umj/article/view/9620.