@unpublished{H89:Theory,
  title = "A Theory of Conjunction and Concurrency",
  author = "C. A. R. Hoare",
  year = "1989",
  month = "may",
  note = "LaTeXed draft, appeared in \textit{A postconference publication based upon the proceedings of PARBASE-90, the First International Conference on Databases, Parallel Architectures and their Applications}, IEEE-CS 1991",
}