Thus, retailers obtain full price for {HEAD ~ products} purchased with {TAIL ~ the exchange system coupons} 
Thus , retailers obtain full price for { HEAD ~ products } purchased with { TAIL ~ the exchange system coupons }
OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL