# How to prove that the limit of surface integral exists?

My book "Electromagnetic Fields" says in $$\text{Section}\ 3.4$$:

Question

Why does the limit in equation $$(3.42)$$ exist (convergent)? Why is the contribution from $$(S-S_{\delta})$$ remains bounded?

I tried to use polar coordinates but still $$|\mathbf{r}-\mathbf{r}'|^{-1}$$ type singularity remains.
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