@article{Klarner1981,
  author    = {{David A. Klarner}},
  title     = {{An algorithm to determine when certain sets have $0$ density}},
  journal   = {{Journal of Algorithms}},
  year      = {{1981}},
  volume    = {{2}},
  pages     = {{31--43}},
  note      = {{MR 84h:10076}},
}