We study bilateral trade between two strategic agents. The celebrated result of Myerson and Satterthwaite states that in general, no incentive-compatible, individually rational and weakly budget balanced mechanism can be efficient. I.e., no mechanism with these properties can guarantee a trade whenever buyer value exceeds seller cost. Given this, a natural question is whether there exists a mechanism with these properties that guarantees a constant fraction of the first-best gains-from-trade, namely a constant fraction of the gains-from-trade attainable whenever buyer's value weakly exceeds seller's cost. In this work, we positively resolve this long-standing open question on constant-factor approximation, mentioned in several previous works, using a simple mechanism.

翻译：我们研究的是两个战略代理商之间的双边贸易。Myerson和Satterthwaite的著名成果指出,一般来说,任何激励兼容、个别合理和预算平衡机制都不可能有效。也就是说,如果买主价值超过卖主成本,任何与这些财产有关的机制都无法保证贸易。有鉴于此,一个自然的问题是,是否有一种机制来保证从贸易中获得的一流收益,即当买主的价值微弱地超过卖主的成本时,从贸易中获得的收益的固定份额。 在这项工作中,我们用一个简单的机制,积极解决以前若干著作中提及的关于常数接近的长期未决问题。