Graph 3D by Eric Piel(Arval.Archi@Wanadoo.fr)

This program permits you to draw 3D functions.
You must enter the function in Y1 with X and Z as variable.
The variations of X and Z are set by modifying Xmin and Xmax (in 'WINDOW')

It destroys I,U,X,Z,'theta' and L5 and L6