Once the portion of the carpet strip that comes into contact with the elevator ropes becomes soiled, the carpet strip can be advanced so that {HEAD ~ a clean portion} of {TAIL ~ the carpet strip} is positioned to be in contact with the elevator ropes and the soiled portion of the carpet strip is discarded 
of
Once the portion of the carpet strip that comes into contact with the elevator ropes becomes soiled , the carpet strip can be advanced so that { HEAD ~ a clean portion } of { TAIL ~ the carpet strip } is positioned to be in contact with the elevator ropes and the soiled portion of the carpet strip is discarded
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 HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH