@misc{ambjorn1994barriers,
  title={Barriers in Quantum Gravity},
  author={Jan Ambjorn},
  year={1994},
  eprint={hep-th/9408129},
  archivePrefix={arXiv},
  primaryClass={hep-th},
  doi={10.1142/9789814447072_0007},
  url={https://arxiv.org/abs/hep-th/9408129}
}