Fraiman, R., Yohai, V.J. and Zamar, R.H. (2001) Optimal robust
M-estimates of location. Ann. Stat. 29(1): 194-223.
M. Kohl (2005). Numerical Contributions to the Asymptotic Theory of Robustness.
Dissertation. University of Bayreuth. https://epub.uni-bayreuth.de/id/eprint/839/2/DissMKohl.pdf.