Skrypnik, W. I. “On the Post-Darwin Approximation of the Maxwell – Lorentz Equations of motion of Point Charges in the Absence of Neutrality”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 71, no. 1, Jan. 2019, pp. 117-28, https://umj.imath.kiev.ua/index.php/umj/article/view/1423.