OsipchukM. M., and PortenkoN. I. “On Simple-Layer Potentials for One Class of Pseudodifferential Equations”. Ukrains’kyi Matematychnyi Zhurnal 67, no. 11 (November 25, 2015): 1512-1524. Accessed December 5, 2020. http://umj.imath.kiev.ua/index.php/umj/article/view/2086.