In many cases, existing ovens can be used as {HEAD ~ the heating source}, without {TAIL ~ modification} 
without
In many cases , existing ovens can be used as { HEAD ~ the heating source } , without { TAIL ~ modification }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH REL TAIL TAIL TAIL TAIL TAIL