The study of \textit{regret minimization in fixed-price bilateral trade} has received considerable attention in recent research. Previous works [CCC+24a, CCC+24b, AFF24, BCCF24, CJLZ25, LCM25a, GDFS25] have acquired a thorough understanding of the problem, except for determining the tight regret bound for GBB semi-feedback fixed-price mechanisms under adversarial values. In this paper, we resolve this open question by devising an $\widetilde{O}(T^{2 / 3})$-regret mechanism, matching the $Ω(T^{2 / 3})$ lower bound from [CJLZ25] up to polylogarithmic factors.

翻译：近年来，关于\textit{固定价格双边交易中的遗憾最小化}研究受到了广泛关注。已有工作[CCC+24a, CCC+24b, AFF24, BCCF24, CJLZ25, LCM25a, GDFS25]对该问题已获得深入理解，唯一遗留的是确定在对抗性估值下GBB半反馈固定价格机制的紧致遗憾界。本文通过设计一个$\widetilde{O}(T^{2 / 3})$遗憾机制，解决了这一开放性问题，该机制与[CJLZ25]中给出的$Ω(T^{2 / 3})$下界在多项式对数因子内匹配。