Varian现代观点chapter 5结尾在讲了从量税和所得税的区别后说所得税对消费者更有利，有下面这么一句话，we have assumed that when we impose the tax on income the consumer's income doesn't change. we have assumed that the income tax is basically a lump sum tax--one that just changes the amount of money a consumer has to spend but doesn't affect any choices he has to make.这句话有点理解不了！高手们讲讲。。。