HeavyWater and SimplexWater: Distortion-free LLM Watermarks for Low-Entropy Distributions - Tsur, Dor; Long, Carol; Mayrink Verdun, Claudio; Vithana, Sajani; Hsu, Hsiang; Chen, Richard; permuter, haim; Calmon, Flavio (Advances in Neural Information Processing Systems, 2025)