Therefore, as {HEAD ~ each vertex} of {TAIL ~ the network graph} is added, a series of constraints for that vertex of the graph is evaluated 
of
Therefore , as { HEAD ~ each vertex } of { TAIL ~ the network graph } is added , a series of constraints for that vertex of the graph is evaluated
OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH