{TAIL ~ The exchange system} invalidates {HEAD ~ a conventional coupon} and prints an exchange system coupon for a product promoted by the coupon exchange system 
{ TAIL ~ The exchange system } invalidates { HEAD ~ a conventional coupon } and prints an exchange system coupon for a product promoted by the coupon exchange system
TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH