Functions for kernel smoothing for Wand & Jones (1995)
c(person("Matt", "Wand", role = "aut", email =
"Matt.Wand@uts.edu.au"), person("Brian", "Ripley", role =
c("trl", "cre", "ctb"), email = "ripley@stats.ox.ac.uk"))
Matt Wand <Matt.Wand@uts.edu.au> R port and updates by Brian
        Ripley <ripley@stats.ox.ac.uk>.
functions for kernel smoothing (and density estimation)
        corresponding to the book: Wand, M.P. and Jones, M.C. (1995)
        "Kernel Smoothing".