An Inference System of an Extension of Floyd-Hoare Logic for Partial Predicates

In the paper we give a formalization in the Mizar system [2, 1] of the rules of an inference system for an extended Floyd-Hoare logic with partial pre- and post-conditions which was proposed in [7, 9]. The rules are formalized on the semantic level. The details of the approach used to implement this formalization are described in [5].

We formalize the notion of a semantic Floyd-Hoare triple (for an extended Floyd-Hoare logic with partial pre- and post-conditions) [5] which is a triple of a pre-condition represented by a partial predicate, a program, represented by a partial function which maps data to data, and a post-condition, represented by a partial predicate, which informally means that if the pre-condition on a program’s input data is defined and true, and the program’s output after a run on this data is defined (a program terminates successfully), and the post-condition is defined on the program’s output, then the post-condition is true.

We formalize and prove the soundness of the rules of the inference system [9, 7] for such semantic Floyd-Hoare triples. For reasoning about sequential composition of programs and while loops we use the rules proposed in [3].

The formalized rules can be used for reasoning about sequential programs, and in particular, for sequential programs on nominative data [4]. Application of these rules often requires reasoning about partial predicates representing preand post-conditions which can be done using the formalized results on the Kleene algebra of partial predicates given in [8].