Skrypnyk, V. I. “Periodic Coulomb Dynamics of Two Equal Negative Charges in the Field of Six Equal Positive Fixed Charges”. Ukrains’kyi Matematychnyi Zhurnal, vol. 72, no. 12, Dec. 2020, pp. 1682-96, https://doi.org/10.37863/umzh.v72i12.917.