The trading of rice warehouse receipts #套利交易策略 is very active. The aforementioned rice warehouse receipts are sold in advance based on future rice harvests, thus becoming the earliest futures contracts in the world. The Dojima Rice Exchange engaged in this type of rice warehouse receipt trading, making it the first futures exchange in the world. Rice warehouse receipts are also known as "empty rice" receipts ("empty rice" means that it is not a specific physical rice).