load(draw);

draw3d(key   = "Gauss",
       color = blue,
         explicit(-2*(x-1)+2*(y-2)+1,x,-3,3,y,-3,3),
       yv_grid = 10,
     color   = red,
       key="Plane",
         explicit(x^2-2*x*y+y^2,x,-5,5,y,-5,5),
       surface_hide = true);