Computing Permutation Encodings

We consider some encodings of permutations of the first N natural numbers, discuss some relations among them and how one can be computed from others. We show a short proof of an existing efficient algorithm for one encoding, and present two new efficient algorithms for encoding permutations. One of these algorithms is constructed as the inverse of an existing algorithm for decoding, making it the first efficient permutation encoding algorithm obtained that way

The Dafny Integrated Development Environment

In recent years, program verifiers and interactive theorem provers have become more powerful and more suitable for verifying large programs or proofs. This has demonstrated the need for improving the user experience of these tools to increase productivity and to make them more accessible to non-experts. This paper presents an integrated development environment for Dafny-a programming language, verifier, and proof assistant-that addresses issues present in most state-of-the-art verifiers: low responsiveness and lack of support for understanding non-obvious verification failures. The paper demonstrates several new features that move the state-of-the-art closer towards a verification environment that can provide verification feedback as the user types and can present more helpful information about the program or failed verifications in a demand-driven and unobtrusive way.Comment: In Proceedings F-IDE 2014, arXiv:1404.578

On computing the fixpoint of a set of boolean equations

This paper presents a method for computing a least fixpoint of a system of equations over booleans. The resulting computation can be significantly shorter than the result of iteratively evaluating the entire system until a fixpoint is reached.Comment: 15 page

Multicomputer Programming with Modula-3D

In this note, we extend an object-oriented language to support programming fine-grain multicomputers. The new constructs have a simple semantics and provide a nice way to write distributed programs. The semantics of the constructs are independent of how a program is distributed. We also show a set of simple conditions under which even the outcome of a program is independent of how its control and data are distributed. We show some strengths and weaknesses of the programming model, and describe and critique our implementation of the language

Extensions to an Object Oriented Programming Language for Programming Fine-grain Multicomputers

In this note, we extend an object-oriented language to support programming fine-grain multicomputers. The new constructs have a simple semantics and provide a nice way to write distributed programs. The semantics of the constructs are independent of how a program is distributed. We also show a set of simple conditions under which even the outcome of a program is independent of how its control and data are distributed

Theory and Use of Conditional Composition

[No abstract available

Dafny meets the Verification Benchmarks Challenge

A suite of verification benchmarks for software verification tools and techniques, presented at VSTTE 2008 [11], provides an initial catalogue of benchmark challenges for the Verified Software Initiative. This paper presents solutions to these eight benchmarks using the language and verifier Dafny. A Dafny program includes specifications, code, inductive invariants, and termination metrics. Each of the eight programs is fed to the Dafny verifier, which without further user interaction automatically performs the verification in a few seconds

Semantics of Exceptions

We describe a trace semantics of exceptions and then derive a weakest precondition semantics. A program that contains exceptions terminates in one of two possible ways (if it terminates at all): either it terminates exceptionally or it terminates normally. We will therefore consider weakest preconditions that are functions of two postconditions. As a preparation we study aribitrary functions of two arguments, and their compositions

Stepwise refinement of heap-manipulating code in Chalice

Stepwise refinement is a well-studied technique for developing a program from an abstract description to a concrete implementation. This paper describes a system with automated tool support for refinement, powered by a state-of-the-art verification engine that uses an SMT solver. Unlike previous refinement systems, users of the presented system interact only via declarations in the programming language. Another aspect of the system is that it accounts for dynamically allocated objects in the heap, so that data representations in an abstract program can be refined into ones that use more objects. Finally, the system uses a language with familiar imperative features, including sequential composition, loops, and recursive calls, offers a syntax with skeletons for describing program changes between refinements, and provides a mechanism for supplying witnesses when refining non-deterministic programs