If the group E is {TAIL ~ a null group}, the flow advances to {HEAD ~ Step} 1 5 
If the group E is { TAIL ~ a null group } , the flow advances to { HEAD ~ Step } 1 5
OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD OTH OTH