@article{Bird89:Algebraic,
  title = "Algebraic Identities for Program Calculation",
  author = "Richard S. Bird",
  year = "1989",
  journal = "Computer Journal",
  month = "apr",
  number = "2",
  pages = "122--126",
  volume = "32",
  doi = "10.1093/comjnl/32.2.122",
}