account for the extended emission of the arc pixel-by-pixel, but we arrived at the conclusion that it is too faint to contribute useful constraints based on our data (compare with Ellithorpe et al. 1996). Thus, we initially used only the coordinates of the images of the core and of G in Table 2 and we excluded the flux ratios as constraints for model fitting.

We also considered object X, which might be: (1) in the foreground of and far from G, and therefore unrelated to the lens system; (2) at about the same redshift as G, implying that its contribution to the lensing must be estimated (note that the $R-I$ color of X lies between that of G and that of the images of the core, and therefore is marginal evidence against X sharing the redshift of G or of the QSO); and (3) in the background of G, and singly-lensed. We consider the last two possibilities below.

We assumed for most of our models that G is the sole contributor to the lensing in the  system (WMS95), save for including object X in one case (see below). We assumed that the center of brightness of G is also its 