The rules for hop count processing are incorrect, in that the implication is
that sending a message with GHC=1 is valid, but this will be decremented to 0 on
receipt and an error message generated (A.4.4.2). 

4.3.4 mixes the question of when to send an error message with the implication
that a node can detect if a loop has been formed (it cannot). We can only be
certain about sending the message.

No guidance is given on how to set the GHC on transmission.

Finally, note that the GHC does not actually prevent looping; it controls
looping (prevents infinite looping).