my_model(x[3], a[1]) { array center[3]; center = [5,5,0]; sp1=hfSphere(x,center,4.); center[2]=-5; sp2=hfSphere(x,center,4.); center[1]=-5; sp3=hfSphere(x,center,4.); center[2]=5; sp4=hfSphere(x,center,4.); my_model = sp1 | sp2 | sp3 | sp4; }