Hi,
These days I am trying to understand a specific equation in the great article "Stephen W. Tsai, Jose Daniel D. Melo, An invariant-based theory of composites, 2014".
The link to the article: https://core.ac.uk/download/pdf/82317096.pdf
If someone know what is the meaning of equation 6 in the article and can share his knowledge I would glad to discuss about it and maybe things will be clarified.

Thanks a lot,
Itay.