# How to reproduce this tensor calculation with Mathematica

The tensor operation shown in the red box is used in the textbook to prove that there are only 9 independent constants for orthotropic materials:

I want to use MMA to reproduce the operation of $$C_ {pqmn} = l_ {ip} ; l_ {jq} ; l_ {km} ; l_ {ln} ; C_ {ijkl}$$ (Where $$C_ {ijkl}$$ is the stiffness tensor), but currently I have no specific idea. I will continue to update the details to make them perfect.