function llh = mymom(z)
global y t
  y1 = y - z(1);
  y2 = y1.*y1   - z(2);
  y3 = y1(2:t,:).*y1(1:t-1,:) - z(3);
  y4 = y1(3:t,:).*y1(1:t-2,:) - z(4);

  y3 = mean(y3)./mean(y2);
  y4 = mean(y4)./mean(y2);

  psi = [mean(y1) mean(y2) mean(y3) mean(y4)]';
  llh = psi'*psi;
  
return;
