. The
               following values of `abcorr' apply to the &quot;reception&quot;
               case in which photons depart from `spoint' at the
               light-time corrected epoch et-lt and *arrive* at the
               observer's location at `et':

                  'LT'       Correct both the position of `spoint' as
                             seen by the observer, and the position
                             of the illumination source as seen by
                             the target, for