In what follows it will be convenient, as a rule, to omit and write A for the aggregate sales of all kinds, A1 for the aggregate sales from one entrepreneur to another and U for the aggregate user costs of the entrepreneurs.

在下文中，通常省略并写 A 代表各种总销售额，A1 代表一个企业家到另一个企业家的总销售额，U 代表企业家的总用户成本，这将是方便的。