[Maxima] Level lines

[Jean-Pierre GERBAL]

Bonjour,

I'am a french mathematic teacher and i need to represent surface and  
level lines with color beetween level lines ;
for example, z=2x^2-x+y^2 (x in 0,10 ; y in 0,10) and one color from  
z=0 to z=25, another color from 25 to 50,....

Is it possible with maxima (i think it is not with gnuplot)

Merci :-)

Jean-Pierre

http://mathazay.free.fr/spip/