- \mu^2} ~~,~~ 
I_5 ~=~ \left. \int_k \frac{(kq)^2}{k^2 (k-p)^2 (k+q)^2} ~~~. \!\!\!\!\!\!\!\! 
\right|_{p^2 \, = \, q^2 \, = \, - \mu^2} \end{aligned}$$ are the basic scalar integrals. This together with the other relevant tensor integrals are substituted back into the main computation and the index contractions are performed. This ensures that no basis tensor is overlooked in the procedure of constructing the basis. Once the basis is established we determine the explicit projection of Appendix A. This is used to check the final results. Moreover, having found the tensor basis at one loop it can then be applied directly in a two loop calculation.

     $i$     $S$   $V$   $T$   $W_2$   $W_3$
  --------- ----- ----- ----- ------- -------
   $n_{i}$   $2$   $6$   $8$   $10$    $14$

[Table 1. Number of projectors for each operator insertion.]{}

In addition, for the $\gamma$-algebra we use the generalized basis of $\gamma$-matrices which has been introduced in [@37; @38; @39] with more explicit details of their properties given in [@40; @41]. Briefly, we define these new matrices, $\Gamma_{(n)}^{\mu_1 \ldots \mu_n}$, by $$\Gamma_{(n)}^{\mu_1 \ldots \mu_n} ~=~ \gamma^{[\mu_1} \ldots \gamma^{\mu_n]}$$ which is totally antisymmetric in the Lorentz indices for $n$ $\geq$ $1$ and the square bracket notation includes the overall 