We've benefited from comments and bug reports from many people on
previous versions of the package. We would like to thank especially :
Arne Henningsen, Christian Kleiber, Katarzyna Kopczewska, Ott Toomet
and Achim Zeileis.

The package was greatly improved during the revision of the Journal of
Statistical Software article, thanks to the helpful comments of three
anonymous referees. We especially thank the co-editor of this journal,
Achim Zeileis, for many interesting comments and suggestions.
