AR-Diffusion: Auto-Regressive Diffusion Model for Text Generation - Wu, Tong; Fan, Zhihao; Liu, Xiao; Zheng, Hai-Tao; Gong, Yeyun; shen, yelong; Jiao, Jian; Li, Juntao; wei, zhongyu; Guo, Jian; Duan, Nan; Chen, Weizhu (Advances in Neural Information Processing Systems, 2023)