BurtnyakI. V., and Malyts’kaH. P. “On the Fundamental Solution of the Cauchy Problem for Kolmogorov Systems of the Second Order”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 70, no. 8, Aug. 2018, pp. 1107-1, https://umj.imath.kiev.ua/index.php/umj/article/view/1621.