Completeness with Finite Systems of Intermediate Assertions for Recursive Program Schemes

Abstract

It is proved that in the general case of arbitrary context-free schemes a program is (partially) correct with respect to given initial and final assertions if and only if a suitable finite system of intermediate assertions can be found. Assertions are allowed from the extended state space $\mathcal {V} \times \mathcal {V}$. This result contrasts with the results of [2], where it is proved that if assertions are taken from the original state space $\mathcal {V}$, then in the general case an infinite system of intermediate assertions is needed. The extension of the state space allows a unification in the relational framework of [2], of the (essence of the) results of [2], and of [4], [5] and [6], and provides a semantic counterpart of the use of auxiliary variables.