\begin{Schunk}
\begin{Sinput}
 x1r <- range(dat$x1)
 x1seq <- seq(x1r[1], x1r[2], length = 30)
 x2r <- range(dat$x2) 
 x2seq <- seq(x2r[1], x2r[2], length=30)
\end{Sinput}
\end{Schunk}
