Thanks Louie for the illustration. It’s really helpful!

In the diagram below “5 Proof of Work” the right hand side (8,9),

the trunkTx should be the hash of (9,9)
the branchTx should be HTQSF9C…0IA999, which is the trunkTx of (9,9)

It seems you simply copy the trunkTx and branchTx from (9,9).

Thanks again.