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