Also included are pairs of {HEAD ~ surfaces} having {TAIL ~ sections} one of which is linear and the other of which is concave: these pairs can be grouped with their plane surfaces in coincidence, and the groups themselves can be further combined 
having
Also included are pairs of { HEAD ~ surfaces } having { TAIL ~ sections } one of which is linear and the other of which is concave : these pairs can be grouped with their plane surfaces in coincidence , and the groups themselves can be further combined
OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL 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 OTH OTH OTH OTH OTH OTH OTH OTH