// --------------
//  The G series
// --------------
height=400;
width =400;
clip=none;
clear_screen;
curve = -(4*(1+x+y)*(y+x+x*y)*x*y-(y+x+x*y)^3
        -4*x^2*y^2)*(16*(y+x+x*y)^5*(1+x+y)^2*x^2
        *y^2+64*(1+x+y)*(y+x+x*y)*x^5*y^5
        -80*(y+x+x*y)^4*(1+x+y)*x^3*y^3
        -8*(y+x+x*y)^7*(1+x+y)*x*y-64*x^6*y^6
        +80*(y+x+x*y)^3*x^4*y^4
        +20*(y+x+x*y)^6*x^2*y^2+(y+x+x*y)^9);
draw_curve;