@inproceedings{forwardbackwardactivationalgorithmfor,
  title = {Forward-Backward Activation Algorithm for Hierarchical Hidden Markov Models},
  author = {Kei Wakabayashi and Takao Miura},
  year = {2012},
  booktitle = {NeurIPS 2012 12},
  url = {http://papers.nips.cc/paper/4628-forward-backward-activation-algorithm-for-hierarchical-hidden-markov-models},
}