\begin{Schunk}
\begin{Sinput}
 plot(x, y, type = "n", main = "Comparing smooth.spline results")
 lines(ss1$x, ss1$y, lty = 1)
 lines(ss2$x, ss2$y, lty = 4)
 lines(ss3$x, ss3$y, lty = 3)
 legend(0.7, -3, c("all.knots=T", "knots=4", "cv=TRUE"), lty = c(1, 4, 3))
 points(x, y, cex = 0.5, col = gray(0.8))
\end{Sinput}
\end{Schunk}
