Basic Action Theory

Action semantics is a semantic description framework with very goodpragmatic properties but until now a rather weak theory for reasoningabout programs. A strong action theory would have a great practicalpotential, as it would facilitate reasoning about the large class ofprogramming languages that can be described in action semantics.This report develops the foundations for a richer action theory, bybringing together concepts and techniques from process theory andfrom work on operational reasoning about functional programs. Semanticpreorders and equivalences in the action semantics setting arestudied and useful operational techniques for establishing contextualequivalences are presented. These techniques are applied to establishequational and inequational action laws and an induction rule

A Complete, Co-Inductive Syntactic Theory of Sequential Control and State

We present a new co-inductive syntactic theory, eager normal form bisimilarity, for the untyped call-by-value lambda calculus extended with continuations and mutable references. We demonstrate that the associated bisimulation proof principle is easy to use and that it is a powerful tool for proving equivalences between recursive imperative higher-order programs. The theory is modular in the sense that eager normal form bisimilarity for each of the calculi extended with continuations and/or mutable references is a fully abstract extension of eager normal form bisimilarity for its sub-calculi. For each calculus, we prove that eager normal form bisimilarity is a congruence and is sound with respect to contextual equivalence. Furthermore, for the calculus with both continuations and mutable references, we show that eager normal form bisimilarity is complete: it coincides with contextual equivalence

Compilation and Equivalence of Imperative Objects (Revised Report)

We adopt the untyped imperative object calculus of Abadi andCardelli as a minimal setting in which to study problems of compilationand program equivalence that arise when compiling object orientedlanguages. We present both a big-step and a small-stepsubstitution-based operational semantics for the calculus. Our firsttwo results are theorems asserting the equivalence of our substitution based semantics with a closure-based semantics like that given by Abadi and Cardelli. Our third result is a direct proof of the correctness of compilation to a stack-based abstract machine via a small-step decompilation algorithm. Our fourth result is that contextual equivalence of objects coincides with a form of Mason and Talcott's CIUequivalence; the latter provides a tractable means of establishing operational equivalences. Finally, we prove correct an algorithm, used inour prototype compiler, for statically resolving method offsets. This isthe first study of correctness of an object-oriented abstract machine,and of operational equivalence for the imperative object calculus

Major Cardiac Events in Patients and Relatives With Hereditary Hypertrophic Cardiomyopathy

BackgroundLittle evidence is available on the disease expression in relatives of index patients with hypertrophic cardiomyopathy (HCM). This information has important implications for family screening programs, genetic counseling, and management of affected families.ObjectivesThe purpose of this study was to investigate the disease expression and penetrance in relatives of index patients carrying pathogenic/likely pathogenic (P/LP) variants in recognized HCM genes.MethodsA total of 453 consecutive and unrelated HCM index patients underwent clinical and genetic investigations. A total of 903 relatives of genotype-positive index patients were invited for clinical investigations and genetic testing. Penetrance, disease expression, and incidence rates of major adverse cardiac events (MACEs) were investigated in individuals carrying P/LP variants.ResultsForty percent (183/453) of index patients carried a P/LP variant. Eighty-four percent (757/903) of all relatives of index patients with P/LP variants were available for the investigation, of whom 54% (407/757) carried a P/LP variant. The penetrance of HCM among relatives was 39% (160/407). Relatives with HCM and index patients were diagnosed at a similar age (43 ± 18 years vs 46 ± 15 years; P = 0.11). There were no differences in clinical characteristics or incidence rates of MACE during 8 years of follow-up.ConclusionsThe disease expression of HCM among index patients and affected relatives carrying P/LP variants in recognized disease genes was similar, with an equal risk of experiencing MACE. These findings provide evidence to support family screening and follow-up of genotype-positive HCM families to improve management and diminish the number of adverse disease complications among relatives

Relational Reasoning about Contexts

The syntactic nature of operational reasoning requires techniques to deal with term contexts, especially for reasoning about recursion. In this paper we study applicative bisimulation and a variant of Sands’ improvement theory for a small call-by-value functional language. We explore an indirect, relational approach for reasoning about contexts. It is inspired by Howe’s precise method for proving congruence of simulation orderings and by Pitts’ extension thereof for proving applicative bisimulation up to context. We illustrate this approach with proofs of the unwinding theorem and syntactic continuity and, more importantly, we establish analogues of Sangiorgi’s bisimulation up to context for applicative bisimulation and for improvement. Using these powerful bisimulation up to context techniques, we give concise operational proofs of recursion induction, the improvement theorem, and syntactic minimal invariance. Previous operational proofs of these results involve complex, explicit reasoning about contexts