断言：使用断言检查字段之间的关系，比如订单中的总量是各行之和。
Assertion: Use assertions to check relationships between fields — for example, the purchase order's total is the sum of the order lines.
产出函数建立了产出的总量或规模与各种投入(比如人力、材料、设备)之间的关系。
A production function relates the amount or volume of output to the various inputs of labor, material and equipment.
同时，劳动生产率变化还会使商品供求关系变化，从而使价值总量发生变化。
The change of labor productivity also can cause the change of the commodity supply and demand relations thus the total value quantity is changed.
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