// --------------
//  The G series
// --------------
height=400;
width =400;
clip=none;
clear_screen;
curve = x*y*((y+x+x*y)^6+8*(y+x+x*y)^3*x^2*y^2
       +8*(1+x+y)^2*(y+x+x*y)^2*x^2*y^2
       -6*(y+x+x*y)^4*(1+x+y)*x*y
       -16*(1+x+y)*(y+x+x*y)*x^3*y^3+8*x^4*y^4);
draw_curve;