@article{Zal-IPL11,
  author = {Eugen Zalinescu},
  title = {Shorter strings containing all $k$-element permutations},
  journal = {Information Processing Letters},
  year = 2011,
  pages = {605--608},
  volume = {111},
  number = {12},
  doi = {10.1016/j.ipl.2011.03.018},
}