Regularisation of VBIE in three-dimensional elastostatics

We regularise the hypersingular integral equation (3.100) using (L.2).

$$\begin{eqnarray*}\lefteqn{\int_{S} \psi_a(\mbox{\boldmath$ x $ }) t^{\infty}_{a}... ...tial \phi_d(\mbox{\boldmath$ y $ })}{\partial y_k} dS_y dS_x \\ \end{eqnarray*}$$