Abbasova, Yu. G., and V. M. Kurbanov. 2017. “the Class $W_{p,m}^1 (G),\; P > 1$, in the Vector Eigenfunctions of a Differential Operator”. Ukrains’kyi Matematychnyi Zhurnal 69 (6), 719-33. https://umj.imath.kiev.ua/index.php/umj/article/view/1731.