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This paper explores the concept of “pure fault tolerance”--when a system can fulfill its computational goal, even though some of its components do not fulfill theirs. This leads to a natural statement of the composition problem for a very general concept of architecture: to what extent are the properties of a system based on that architecture a function of(More)
This paper is a progress report on an experimental system, the state delta verification system (SDVS), for verifying microcode correctness. The goal of this project is to solve some of the problems, both theoretical and engineering, obstructing the realization of a usable and applicable program for checking proofs of microcode correctness. The ideal result(More)
We examine the common and seemingly simple specification that the output stream equals the input stream. We show that this is not in full generality expressible in first-order or temporal logic by an infinite set of sentences or a recursive specification, but requires certain extra assumptions, such as the existence of a clock or discrete input values. The(More)
Equality data bases are important in facilitating proofs of equality between terns. They are useful in the implementation of code optimizers [2], program verifiers [7,9], theorem provers [I], and symbolic execution systems [S]. In these applications the typical operations are determining whether or not two terms are known to be equal and updating the data(More)