First of all, commodities exist. Only when you own the goods first can you have the right to sell and dispose of them. People can sell delivery by producing, buying or even borrowing cash; Or buy for delivery in the near future and sell for delivery in the long term. This is a normal process, so we are used to calling it positive set.

If you don't have the goods in advance, you can't deliver them when you sell them in the latest contract. The irreversibility of time can't make the future ownership meet the present pay, so the process of' selling in the near future and buying in the long term' in the futures market is relatively reverse, which we call hedging.

From the perspective of free trade, commodity prices are low in areas with abundant supply and demand and high in areas with insufficient supply and demand, so commodities should flow from areas with abundant supply and demand to areas with insufficient supply and demand. Judging from the domestic supply and demand situation, crude oil, soybeans, copper, rubber and other varieties are in short supply and need to be imported. Their flow is basically to buy abroad and sell at home. Therefore, LME buys copper and throws it at Shanghai copper, which is habitually called positive plate; Buying CBOT soybeans and selling Dalian soybeans is also called matching. This kind of positive matching transaction can be transformed into actual import trade, while the reverse matching transaction cannot be transformed into actual trade due to obstacles or losses caused by export policies, which is also an alternative meaning of' pros and cons' in this kind of transaction.