my_model(x[3], a[1])
{
array xt[3], x0[3];
xt[1]=x[1];
xt[2]=x[2];
xt[3]=x[3];

sp1 = 1-(xt[1]/2)^4- (xt[2]/8)^4- (xt[3]/2)^4; 

x0=[6,-8, 0];
tmp = hfStretch3D(xt,x0,1,0.3,1);
xt[1]=xt[1]-6;
sp2 = 1-(xt[1]/2)^4- (xt[2]/8)^4- (xt[3]/2)^4;

xt[1]=x[1];
xt[2]=x[2];
xt[3]=x[3];
xt[1]=xt[1]+6;
x0=[0, 0, 0];
tmp = hfStretch3D(xt,x0,1.5,0.5,2);
sp3 = 1-(xt[1]/2)^4- (xt[2]/8)^4- (xt[3]/2)^4;

my_model = sp1 | sp2 |sp3;
}