As stated originally, the venerable law of one price succinctly describes long-run equilibrium in a perfectly competitive market. The law was later amended, defining a market as the geographic area within which the same thing sells for the same price at the same time, allowance being made for...

The Alchian and Allen theorem predicts that it will be harder to find "good" apples in the State of Washington, a prime apple-growing region, than in, say, New York City, where the addition of shipping charges makes "bad" apples comparatively more expensive. We recast the theorem as a testable...