@article{Marcinkowski1999,
  author    = {{Jerzy Marcinkowski}},
  title     = {{Achilles, Turtle, and Undecidable Boundedness Problems for Small DATALOG programs}},
  journal   = {{SIAM J. Comput.}},
  year      = {{1999}},
  volume    = {{29}},
  pages     = {{231--257}},
  note      = {{MR 2002d:68035}},
}