“…Paraphrase Generation has proven to be useful for adversarial training and data augmentation (Zhou and Bhat, 2021). Early methods adopt hand-crafted rules (McKeown, 1983), synonym substitution (Bolshakov and Gelbukh, 2004), machine translation (Quirk et al, 2004), and deep learning (Gupta et al, 2018; to improve the quality of generated sentences. To acquire syntactic diverse samples, recent studies involve reinforcement learning (Qian et al, 2019) or syntactic constrains (Iyyer et al, 2018;Goyal and Durrett, 2020;Sun et al, 2021) into the models.…”