Айсагалиев, С. А., Б. К. Абенов, and А. М. Аязбаева. “ To Absolute Stability of the Regular Systems in the Critical Case”. Journal of Mathematics, Mechanics and Computer Science, vol. 83, no. 4, Dec. 2014, pp. 12-30, https://bm.kaznu.kz/index.php/kaznu/article/view/75.