@misc{W2121227244,
  author = {Peter F. Brown and P.V. deSouza and Robert L. Mercer and Vincent J. Della Pietra and Jenifer C. Lai},
  title = {Class-based n -gram models of natural language},
  year = {1992},
  doi = {https://doi.org/10.5555/176313.176316}
}