Byron, FW., Joachain, CJ., & Piraux, B. (1986). Theory of Coplanar Asymmetric (e, 2e) Reactions in Helium. Journal of Physics B: Atomic, Molecular and Optical Physics, 19(8), 1201-1210. https://doi.org/10.1088/0022-3700/19/8/015 (Original work published 1986)