Cushion

$\begin{figure}\begin{center}\BoxedEPSF{Cushion.epsf}\end{center}\end{figure}$

The Quartic Surface resembling a squashed round cushion on a barroom stool and given by the equation

$\begin{displaymath} z^2x^2-z^4-2zx^2+2z^3+x^2-z^2-(x^2-z)^2-y^4-2x^2y^2-y^2z^2+2y^2z+y^2=0. \end{displaymath}$

References