\magnification=\magstep1

$$
{\theta}_E \quad = \quad \sqrt{  { 4 G M } \over { D c^2 } } 
$$


$$
{D}_{\Delta t} \quad = \quad (1 + z_{\rm L}) 
                     \left( { {D_{\rm L}}{D_{\rm S}} } \over {D_{\rm LS} } 
                     \right) 
$$



\bye
