a modified model A that included X in this fashion. We found $\chi^2/DOF\sim 41$ for this model, a very significantly worse fit than for our other models. Because X is clearly not point-like, we infer that it may be a dwarf galaxy near the redshift of G, or in its foreground.

Conclusions
===========

We conclude first that lensing is compellingly confirmed for , in spite of the lack of a measured redshift for the lens galaxy. It seems very probable that the arc that we discovered is a highly magnified and distorted image of a patch of the source near its core. Together with the morphology of the images of the core, as refined by our observations, the arc is strong evidence in favor of lensing.

Our observations yielded positions for all 4 known images of the QSO central core, with standard errors of $0\farcs02$, and for the lens galaxy G with standard errors of $0\farcs05$; our $R$ and $I$ photometry for these objects has standard errors $\sim 0.01$ mag. The photometry of the arc is much less accurate ($\sim 0.3$ mag standard errors), because it is extremely faint, especially in the $R$ filter.

The brightness distribution of G is 