Adrian W. Bowman and Adelchi Azzalini.
Ported to R by B. D. Ripley <ripley@stats.ox.ac.uk> up to version 2.0,
later versions by Adrian W. Bowman and Adelchi Azzalini.
This is software linked to the book
`Applied Smoothing Techniques for Data Analysis:
The Kernel Approach with S-Plus Illustrations' Oxford University Press.
Smoothing methods for nonparametric regression and density estimation