Akhmetov, M. U., and R. D. Seilova. “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, Vol. 52, no. 6, June 2000, pp. 723–730, https://umj.imath.kiev.ua/index.php/umj/article/view/4466.