The Law of One Price: This principle is the beginning of currency valuation and it goes back over half a millennium.

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In other words, the Law of One Price refers to the profit margins, or the excess of price over cost, and not just the price.

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Since the rise of the modern nation-state, classical economists have had to reason further from the Law of One Price, pointing out that the Law of One Price is a law of market-based economies and that the law becomes distorted as the market become distorted by forcible interruptions in transnational exchanges.

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But it is a nice object lesson in the basic economic proposition first put forward by David Ricardo as the Iron Law of One Price.

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Ricardo called this the iron law of one price.

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