forming {HEAD ~ a second difference} which is {TAIL ~ a function} of the second model temperature and the first model temperature, and 
is
forming { HEAD ~ a second difference } which is { TAIL ~ a function } of the second model temperature and the first model temperature , and
OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH