The Lerner symmetry theorem is a result used in

international trade International trade is the exchange of capital, goods, and services across international borders or territories because there is a need or want of goods or services. (see: World economy) In most countries, such trade represents a significa ...

theory, which states that an

ad valorem An ''ad valorem'' tax (Latin for "according to value") is a tax whose amount is based on the value of a transaction or of property. It is typically imposed at the time of a transaction, as in the case of a sales tax or value-added tax (VAT). An ...

import tariff (a percentage of value or an amount per unit) will have the same effects as an export tax. The theorem is based on the observation that the effect on relative prices is the same regardless of which policy (ad valorem tariffs or export taxes) is applied. The theorem was developed by economist Abba P. Lerner in 1936. Jagdish N. Bhagwati,

Arvind Panagariya Arvind Panagariya (born 30 September 1952) is an Indian-American economist who is the Jagdish Bhagwati Professor of Indian Political Economy at Columbia University and is also the Director of Deepak and Neera Raj Center on Indian Economic Polic ...

, and

T. N. Srinivasan T. N. Srinivasan, in full Thirukodikaval Nilakanta Srinivasan (27 March 1933 – 11 November 2018), was an Indian economist who had taught and worked in the United States. He was the Emeritus Samuel C. Park, Jr. Professor of Economics at Yale ...

, 1998 ''Lectures On International Trade'', 2nd Edition, MIT Press
Description
and ch. 12, sect. 12-6, Lerner Symmetry Theorem, scrollable preview, pp
215-19.
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Notes

References

Economics theorems {{econ-stub