@misc{indiciae1826e69ea1d0,
  title = {Bidirectional sticker systems.},
  author = {R Freund and G Păun and G Rozenberg and A Salomaa},
  year = {1998},
  url = {https://pubmed.ncbi.nlm.nih.gov/9697210/},
  note = {Source identifier: 9697210}
}