一、Critical conceptions

（一）CS

1. Willingness to pay

demand curve等同于 marginal willingness to pay（MWTP）

2. Consumer surplus

Consumer surplus (CS) = Total WTP ⎼ Payment

可以使用CS作为效用变化的近似值

（二）Measuring utility change

1. Compensating variation

Definition：How much money we would have to give the consumer after the change to make him/her just as well off as he/she was before the change

2. Equivalent variation

Definition：How much money would have to betaken away from the consumer before the change to leave him/her just as well off as he would be after the change

（三）Demand Curve

1. Different demand curves

• Standard demand curve 标准需求曲线：also called Marshallian or Walrasian demand curve,keeps income fixed