A^2Search: Ambiguity-Aware Question Answering with Reinforcement Learning - Zhang, Fengji; Niu, Xinyao; Ying, Chengyang; Lin, Guancheng; Hao, Zhongkai; Fan, Zhou; Huang, Chengen; Keung, Jacky; Chen, Bei; Lin, Junyang (International Conference on Learning Representations, 2026)