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