{HEAD ~ The presence} of {TAIL ~ the gap} 602 and the absence of a gap 601 indicates that replacement of the consumable part 605 is necessary 
of
{ HEAD ~ The presence } of { TAIL ~ the gap } 602 and the absence of a gap 601 indicates that replacement of the consumable part 605 is necessary
HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH