Study of theoretical luminosity precision for electron colliders at higher energies S. Jadach, W. Płaczek, M. Skrzypek and B. F. L. Ward Eur. Phys. J. C, 81 11 (2021) 1047 Published online: 30 November 2021 DOI: 10.1140/epjc/s10052-021-09860-9