Therefore, a proper replacement can be achieved at the latter step S151 by making {HEAD ~ the profiles} at {TAIL ~ the line L side} coincide together 
at
Therefore , a proper replacement can be achieved at the latter step S151 by making { HEAD ~ the profiles } at { TAIL ~ the line L side } coincide together
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 TAIL TAIL OTH OTH