In calculating a route through a network of nodes and links, {HEAD ~ a standard constrained shortest path first method} builds {TAIL ~ a network graph}, accumulating a set of path data 
builds
In calculating a route through a network of nodes and links , { HEAD ~ a standard constrained shortest path first method } builds { TAIL ~ a network graph } , accumulating a set of path data
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH