Tensor coupling and 6j/9j symbols

[Yoran91]

Hi everyone,

I'm reading about the Wigner-Eckhart Theorem and the coupling of spherical tensor operators in Sakurai's Advanced Quantum Mechanics.
I then came across this http://cc.oulu.fi/~tf/tiedostot/pub/kvmIII/english/2004/09_tensop.pdf, which states these concepts in Theorem 1 and 3.

I'm now trying to find a connection between this coupling of tensor operators and 6j and 9j symbols. In the above document, such a link is established in the very last line, but I don't quite understand it. Nothing like this is mentioned in Sakurai and I can't find any other source that provides how these things are connected.

Is there a good source discussing this?
Thanks in advance for any help

 

[Bill_K]

It's derived (more or less) in the "Angular Momentum in Quantum Mechanics" book by Edmonds. Sect 7.1, Matrix Elements of the Tensor Product of Two Tensor Operators.