This document is short and clear and easy to understand for someone who has a basic understanding of BIER. I do have one minor issue that probably needs to get addressed/clarified

* Section 3:

Step 3: "If BA is NULL" -> What exactly does this mean? Does this mean BAR==0? If so, it might be good to state this explicitly and I suggest pulling forward the text from Section 3.1. to clarify BAR==0 means that BA is NULL and BC is NULL. If not, can you please clarify? i.e. do you expect there to be a NULL BA with a BAR<>0?