Luxuries Are Easier to Postpone: A Proof
证明在商品可加性分离条件下，收入弹性与自身价格弹性成正比，这意味着奢侈品更容易被推迟消费，并指出常替代弹性偏好可能不适用于消费。
We show that (Marshallian) income elasticities are proportional to (Frisch) own price elasticities if all goods are additively separable. This implies that luxuries are likely to be easier to postpone. It also implies that preferences over "consumption" are unlikely to display a constant elasticity of substitution.