The buffer element 14 has {HEAD ~ a first edge} 141 and {TAIL ~ a second edge} 142 disposed oppositely to each other 
The buffer element 14 has { HEAD ~ a first edge } 141 and { TAIL ~ a second edge } 142 disposed oppositely to each other
OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH