@article{BinaryDigitalPictures,
  title = "A theory of binary digital pictures",
  author = "A. W. Roscoe and T.Y. Kong",
  year = "1985",
  journal = "Computer Vision, Graphics and Image Processing",
  month = "November",
  number = "32",
  pages = "221--243",
  url = "http://www.cs.ox.ac.uk/people/bill.roscoe/publications/13.pdf",
}