1. Free Generation
   1. [1]. GPT/GPT-2
   2. [2]. BERT for NLG
2. Conditional Generation
   1. [3]. mircosoft: MASS
   2. [4]. mircosoft: UNIFM
   3. [5]. AI2: GROVER
   4. [6].Pretraining for Conditional Generation with Pseudo Self Attention
3. Decoding Method
   1. Autoregressive
      1. seq2seq, transformer
   2. Non-AutoRegressive
      1. [8] Non-Autoregressive NMT
      2. [9]. InDIGO
      3. [10]. Insertion Transformer
      4. [11]. Levenshtein Transformer
      5. [12]. based on masked LM
4. RL+GAN
   1. [13, 14]. seqgan/ RAML
   2. [15, 16]. ScratchGAN/ COT
5. Metric
   1. F-score/accuracy
   2. BLEU for MT, ppl
   3. [7]. SJTU :Texygen
6. [13]. train-test skewness, exposure bias
7. Pre-training for NLG