ORIGAMISPACE: Benchmarking Multimodal LLMs in Multi-Step Spatial Reasoning with Mathematical Constraints - Xu, Rui; Lu, Dakuan; Zhao, Zicheng; Tan, Xiaoyu; Wang, Xintao; Yuan, Siyu; Chen, Jiangjie; xu, yinghui (Advances in Neural Information Processing Systems, 2025)