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