Consider the Henon mapping (13.5) with $a=1.4$ and $b=0.3$. Show that the quadrilateral $D$ with vertices $(1.32,0.133),(-1.33,0.42),(-1.06,-0.5)$ and $(1.245,-0.14)$ is mapped into itself by $f$. Use a computer to plot the iterates of a typical point in $D$.