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