Note on algorithm 21

J. van der Wal. Note on algorithm 21. Computing, 17(3):261-264, 1976. [doi]

@article{Wal76a,
  title = {Note on algorithm 21},
  author = {J. van der Wal},
  year = {1976},
  doi = {10.1007/BF02259650},
  url = {http://dx.doi.org/10.1007/BF02259650},
  researchr = {https://researchr.org/publication/Wal76a},
  cites = {0},
  citedby = {0},
  journal = {Computing},
  volume = {17},
  number = {3},
  pages = {261-264},
}