Boichuk А. A., et al. “Solutions of Weakly-Perturbed Linear Systems Bounded on the Entire Axis”. Ukrains’kyi Matematychnyi Zhurnal, vol. 54, no. 11, Nov. 2002, pp. 1517-30, https://umj.imath.kiev.ua/index.php/umj/article/view/4189.