be noted that there are two other EROs (“A” and “C”) within 10of the sub-mm source.

Discussions
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Lens Model and Surface Density Calculation
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As shown in figure 3 and figure 4, there are concentrations of EROs within a small area in both fields. For discussing the surface-density enhancement, it is not straightforward to compare our sample with other wide-field ERO surveys, because our observation is targeted to the fields of cluster of galaxies. The effects by gravitational lensing, such as amplification of the source flux and the accompanying distortion of the background sky (source plane), should be taken into account. In such a case, lensing models can be used to compute the lens amplification as a function of the image plane position.

We modeled lensing clusters using an elliptical potential with the parameters listed in table 2. The lensing inversion was based on the prescription of Kormann et al. (1994) and Schneider et al. (1992), allowing calculations of the lensing amplification and distortion as a function of the position in the image plane. The essential parameters of the model are the redshift and the line-of-sight velocity dispersion of the cluster. The cluster ellipticity ($f$ in table 2.) is 