Semantical analysis of specification logic, 3 - An operational approach

We are presenting a semantic analysis of Reynolds's specification logic of Idealized Algol using the parametric operational techniques developed by Pitts. We hope that this more elementary account will make the insights of Tennent and O'Hearn, originally formulated in a functor- category denotational semantics, more accessible to a wider audience. The operational model makes clearer the special nature of term equivalence in the logical setting, identifies some problems in the previous interpretation of negation and also proves the soundness of two new axioms of specification logic. Using the model we show that even a very restricted fragment of specification logic is undecidable.