@InProceedings{CavalcantWoodcock02,
  title =        "{A} {P}redicate {T}ransformer {S}emantics for a {C}oncurrent {L}anguage of {R}efinement",
  author=        "Cavalcanti,  Ana and Woodcock,  Jim",
  editor=        "Pascoe,  James S. and Loader,  Roger J. and Sunderam,  Vaidy S.",
  pages =        "147--166",
  booktitle=     "{C}ommunicating {P}rocess {A}rchitectures 2002",
  isbn=          "1 58603 268 2",
  year=          "2002",
  month=         "sep",
  abstract=      "Circus is a combination of Z and CSP; its chief
     distinguishing feature is the inclusion of the ideas of the
     refinement calculus. Our main objective is the definition of
     refinement methods for concurrent programs. The original
     semantic model for Circus is Hoare and He's unifying
     theories of programming. In this paper, we present an
     equivalent semantics based on predicate transformers. With
     this new model, we provide a more adequate basis for the
     formalisation of refinement and verification-condition
     generation rules. Furthermore, this new framework makes it
     possible to include logical variables and angelic
     nondeterminism in Circus. The consistency of the relational
     and predicate transformer models gives us confidence in
     their accuracy."
}