Distilling the Thought, Watermarking the Answer: A Principle Semantic Guided Watermark for Reasoning Large Language Models - Liu, Shuliang; Li, Xingyu; Liu, Hongyi; Fang, Dong; Duan, Bingchen; Qi, Zheng; Su, Lingfeng; Hu, Xuming (International Conference on Learning Representations, 2026)