{HEAD ~ The segmentation} also may define {TAIL ~ points} at which aggregate outputs may be provided, and where checkpoints may be established 
define
{ HEAD ~ The segmentation } also may define { TAIL ~ points } at which aggregate outputs may be provided , and where checkpoints may be established
HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH