Also included are {TAIL ~ pairs} of {HEAD ~ surfaces} having 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 
Also included are { TAIL ~ pairs } of { HEAD ~ surfaces } having 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 TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD 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 OTH OTH