Akhmetov, M. U., and R. D. Seilova. 2000. “Rank Criteria for the Controllability of a Boundary-Value Problem for a Linear System of Integro-Differential Equations With Pulse Influence”. Ukrains’kyi Matematychnyi Zhurnal 52 (6), 723–730. https://umj.imath.kiev.ua/index.php/umj/article/view/4466.