p:价格price 利润profit

q:数量（产销量）quantity

d:需求demand

s:供给supply

e:均衡（或期望）equilibrium

u:效用utility

tu:total utility总效用

mu:marginal utility 边际效用

cs:consumer surplus 消费者剩余

mrs:商品的边际替代率marginal rate of substitution