What is meant by mutual possession (taqabud) in the sale of usurious items—when the genus is the same—if the sold item is a commodity for a commodity, and what do they take possession of?

The exchange of usurious commodities requires that the exchange takes place in the contracting session before separation. So, if dates are sold for dates, equality and immediate possession in the session are required. If dates are sold for salt, immediate possession in the session is required.