A production line has {TAIL ~ a plurality} of working groups in which work operations are controlled by {HEAD ~ a sequential controller} 
A production line has { TAIL ~ a plurality } of working groups in which work operations are controlled by { HEAD ~ a sequential controller }
OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD