English: Cournot dupoly: best response functions and isoprofit curves.

Created with wxmaxima and enhanced with Gimp and Inkscape:

implicit_plot([y=(100-x)/2,x=(100-y)/2,
(100-x-y)*x=10000/9,(100-x-y)*x=10000/6,(100-x-y)*x=10000/13.5,
(100-x-y)*y=10000/9,(100-x-y)*y=10000/6,(100-x-y)*y=10000/13.5],
[x,0,100],[y,0,100],
[style,[lines,1,3],[lines,3,1],
[lines,3,2],[lines,3,5],[lines,1,4],
[lines,1,3],[lines,3,5],[lines,1,4]],
[legend, "2 enpresaren erreakzio-funtzioa", "1 enpresaren erreakzio-  funtzioa",
"Orekako isomozkin-kurba","Mozkin handiagoko isomozkin-kurba",
"Mozkin txikiagoko isomozkin-kurba",
"Orekako isomozkin-kurba","Mozkin handiagoko isomozkin-kurba",
 "Mozkin txikiagoko isomozkin-kurba"]);

After creation, some legends were removed and axis labels were added with image editor.