a cord shaped or tape shaped stopper having {HEAD ~ a first end portion} and {TAIL ~ a second end portion}, the first end portion being fixed to the cover; and 
a cord shaped or tape shaped stopper having { HEAD ~ a first end portion } and { TAIL ~ a second end portion } , the first end portion being fixed to the cover ; and
OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH