The C code for Qn() and Sn(), src/qnsn.c is based on Fortran code
that has been be available from
  http://www.agoras.ua.ac.be/ (Antwerp Group On Robust & Applied Statistics)
   (-> Programs -> Robust)
by {at the time}
    Peter Rousseeuw (rousse@wins.uia.ac.be)
    Christophe Croux (croux@wins.uia.ac.be)
		Department of Mathematics and Computing
		Universitaire Instelling Antwerpen
		Universiteitsplein 1
		B-2610 Wilrijk (Antwerp)
		Belgium

and carries the note

   This file contains fortran functions for two new robust estimators
   of scale denoted as Qn and Sn, decribed in Rousseeuw and Croux (1993).
   These estimators have a high breakdown point and a bounded influence
   function. The implementation given here is very fast (running in
   O(n logn) time) and needs little storage space.

	Rousseeuw, P.J. and Croux, C. (1993)
	Alternatives to the Median Absolute Deviation",
	Journal of the American Statistical Association, Vol. 88, 1273-1283.

   This software may be used and copied freely for scientific
   and/or non-commercial purposes, provided reference is made
   to the above mentioned paper.

where as Martin Maechler got explicit permission from P.Rousseeuw to
licence it under the GNU Public Licence.
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