Control over borders and access to the common market were key issues in the Brexit negotiations concerning the UK's future relationship with the European Union (EU). The parties have expressed strong political commitments regarding both issues. We explore a sequential model, which allows us to analyze the effects of these commitments. It is assumed that the UK controls labor mobility, and that the EU can constrain trade to dissuade future secession, or to punish the UK. We find that the EU has an incentive to claim trade and mobility to be inseparable freedoms whether that reflects its true preferences or not. Our model also implies that both parties are better off if the UK commits to a mobility policy first. Moreover, UK contributions to the EU budget can substitute for trade restriction and allow for a more efficient outcome. Finally, while the EU lacks bargaining power without a readiness to impose trade restrictions, a stronger will to punish the UK does not affect mobility but harms trade. Hence, fueling resentment about Brexit does not benefit the EU.

中文翻译：

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英国退欧：如何达成友好离婚*

边界控制和进入共同市场是英国脱欧谈判中有关英国与欧盟（EU）未来关系的关键问题。双方已就这两个问题表达了强烈的政治承诺。我们探索了一个顺序模型，它使我们能够分析这些承诺的影响。假设英国控制劳动力流动，欧盟可以限制贸易以阻止未来的分裂，或惩罚英国。我们发现欧盟有动力将贸易和流动性视为不可分割的自由，无论这是否反映了其真正的偏好。我们的模型还暗示，如果英国首先承诺实施流动性政策，那么双方都会过得更好。此外，英国对欧盟预算的贡献可以替代贸易限制并产生更有效的结果。最后，虽然欧盟缺乏议价能力，不准备实施贸易限制，但更强烈的惩罚英国的意愿不会影响流动性，但会损害贸易。因此，加剧对英国退欧的不满对欧盟不利。