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Reference:
Unified inter and intra options learning using policy gradient methods K. Y. Levy, N. ShimkinIn European Workshop on Reinforcement Learning, 2011
Bibtex Entry:
@inproceedings{levy2011unified,
  title={Unified inter and intra options learning using policy gradient methods},
  author={Levy, Kfir Y and Shimkin, Nahum},
  booktitle={European Workshop on Reinforcement Learning},
  pages={153--164},
  year={2011},
  organization={Springer}
}