A seat includes {HEAD ~ a base} having {TAIL ~ a block} extended rearward for forming a pair of notches 
having
A seat includes { HEAD ~ a base } having { TAIL ~ a block } extended rearward for forming a pair of notches
OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH