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