V. Y. Slyusarchuk, “Necessary and sufficient conditions for the absolute instability of solutions of linear differential-difference equations with self-adjoint operator coefficients”, Ukr. Mat. Zhurn., vol. 70, no. 5, pp. 715–724, May 2018, Accessed: Dec. 06, 2025. [Online]. Available: https://umj.imath.kiev.ua/index.php/umj/article/view/1590