Sources

• Huang et. al., 2015 (LSTM-CRF)
• Chiu & Nichols, 2015 (CNN-LSTM-CRF)
• Lample et. al., 2016 (LSTM-CRF w/ LSTM char-level features)
• Ma & Hovy, 2016 (CNN-LSTM-CRF)
• Peters et. al., 2017
• Liu et. al., 2017 (LM-LSTM-CRF)