surface orange_crescent2(float    Kfb = 1, 
                        radius = 0.4,
                        s1 = 0.5,
                        s2 = 0.4,
                        t1 = 0.5,
                        t2 = 0.4)
{
color    surfcolor = 1;
  
if (((s-s1)*(s-s1) + (t-t1)*(t-t1) <= radius*radius) && ((s-s2)*(s-s2) + (t-t2)*(t-t2) >= radius*radius))
    surfcolor = color(1, 0.5, 0);
    
Oi = Os;
  
Ci = Oi * Cs * surfcolor * Kfb;
}