t / t4034 / bibtex / preon commit pack_if_possible_fn(): use ref_type() instead of is_per_worktree_ref() (a935ebd)
   1@article{aldous1987uie,
   2  title={{Ultimate instability of exponential back-off protocol for acknowledgment-based transmission control of random access communication channels}},
   3  author={Aldous, D.},
   4  journal={Information Theory, IEEE Transactions on},
   5  volume={33},
   6  number={2},
   7  pages={219--223},
   8  year={1987},
   9}