defining the model variable for the air mass flow into the cylinder as {HEAD ~ a linear function} of {TAIL ~ the inlet pipe pressure}; and 
defining the model variable for the air mass flow into the cylinder as { HEAD ~ a linear function } of { TAIL ~ the inlet pipe pressure } ; and
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 TAIL OTH OTH