Byron, FW., Joachain, CJ., & Potvliege, RM. (1981). Unitarization of the Eikonal-born Series Method for Electron-atom and Positron-atom Collisions. Journal of Physics B: Atomic, Molecular and Optical Physics, 14(19), L609-L615. https://doi.org/10.1088/0022-3700/14/19/005 (Original work published 1981)