Quadrifolium

$\begin{figure}\begin{center}\BoxedEPSF{Quadrifolium.epsf scaled 700}\end{center}\end{figure}$

The Rose with . It has polar equation

$\begin{displaymath} r = a \sin(2\theta), \end{displaymath}$

and Cartesian form

$\begin{displaymath} (x^2+y^2)^3 = 4a^2 x^2 y^2. \end{displaymath}$