[pstricks] how can I do transparent a solid?

[mary montenegro]

Hello!
I would like to be able to use pstricks solides-3d to draw a transparent solid.
I have successfully constructed a graph using this code:

\begin{pspicture}[showgrid=false](-4,-2)(3,3.5)
 \psset{viewpoint=100 27.5 20,Decran=60}
 \psSolid[object=face,base=0 -3 9 -3  9 3 0 3,action=draw*,fillcolor=white,linestyle=dashed]
 \defFunction{F}(t){t 2 exp}{t}{}
 \psSolid[object=face,base=3 -3 {F} CourbeR2+,resolution=360,action=draw]
 \psSolid[object=face,base=3.25 3 {F} CourbeR2+,resolution=360,action=draw]
 \psSolid[object=face,base=-3 -3.25 {F} CourbeR2+,resolution=360,action=draw]
 \psSolid[object=plan,definition=equation,args={[1 0 0 -9]},base=-5 0 -3 3,action=draw*,
 fillcolor=gray!20,fillstyle=opacity]% this is the solid that I need to be transparnt
 \axesIIID[showOrigin=true](0,-5,0)(14,4,5)
\end{pspicture}

It constructs a parbola in the plane xy and a parallel plane to axes z.
The plane is gray color and it don't  permit see the parabola.

How can I do visible the parabola with this gray plane above?

Thanks!

 		 	   		  
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