On the Logic of TLA+

TLA+ is a language intended for the high-level specification of reactive, distributed, and in particular asynchronous systems. Combining the linear-time temporal logic TLA and classical set-theory, it provides an expressive specification formalism and supports assertional verification

Model-checking Secure Information Flow for Multi-Threaded Programs

Abstract. This paper shows how secure information flow properties of multi-threaded programs can be verified by model checking in a precise and efficient way, by using the idea of self-composition. It discusses two properties that aim to capture secure information flow for multi-threaded programs, and it shows how these properties can be char-acterised in modal µ-calculus. For this characterisation, a self-composed model of the program is constructed. More precisely, this is a model that contains two copies of the labelled transition system induced by the program, so that the program is executed in parallel with itself. The self-composed model allows to compare two program executions in a single temporal formula that characterises a secure information flow property. Both the formula and model are translated into the input language for the Concurrency Workbench model checker. We discuss this encoding, and use it for some practical experiments on several simple examples.

Reasoning about correctness properties of a coordination programming language

Safety critical systems place additional requirements to the programming language used to implement them with respect to traditional environments. Examples of features that in uence the suitability of a programming language in such environments include complexity of de nitions, expressive power, bounded space and time and veri ability. Hume is a novel programming language with a design which targets the rst three of these, in some ways, contradictory features: fully expressive languages cannot guarantee bounds on time and space, and low-level languages which can guarantee space and time bounds are often complex and thus error-phrone. In Hume, this contradiction is solved by a two layered architecture: a high-level fully expressive language, is built on top of a low-level coordination language which can guarantee space and time bounds. This thesis explores the veri cation of Hume programs. It targets safety properties, which are the most important type of correctness properties, of the low-level coordination language, which is believed to be the most error-prone. Deductive veri cation in Lamport's temporal logic of actions (TLA) is utilised, in turn validated through algorithmic experiments. This deductive veri cation is mechanised by rst embedding TLA in the Isabelle theorem prover, and then embedding Hume on top of this. Veri cation of temporal invariants is explored in this setting. In Hume, program transformation is a key feature, often required to guarantee space and time bounds of high-level constructs. Veri cation of transformations is thus an integral part of this thesis. The work with both invariant veri cation, and in particular, transformation veri cation, has pinpointed several weaknesses of the Hume language. Motivated and in uenced by this, an extension to Hume, called Hierarchical Hume, is developed and embedded in TLA. Several case studies of transformation and invariant veri cation of Hierarchical Hume in Isabelle are conducted, and an approach towards a calculus for transformations is examined.James Watt ScholarshipEngineering and Physical Sciences Research Council (EPSRC) Platform grant GR/SO177

Towards a Mobile Temporal Logic of Actions

I would like to thank my supervisor Fred Kröger. He was willing to discuss at any time, and I could always rely on his full support. I am also thankful to him for his encouragement, especially in some of the rather dragging phases of my work. I am particularly grateful to Stephan Merz. Without his constant support and admirable patience throughout the whole period of writing I probably would not have been able to finish this thesis. I have not only benefited from his extraordinary professional competence, but have also taken advantage of his exceptional human qualities. I also would like to express my gratitude towards Martin Wirsing for providing me with a pleasant working environment by taking me into his group. He always has shown much interest in my work. The idea for the subject of this thesis was initiated by him and Stephan Merz. I feel a need to thank all my friends and my family for not leaving me alone, not even in times when I tended to be almost unbearable... I am aware that I have demanded much of you by asking to share the burden with me. Thank you for no

Synthesis from multi-paradigm specifications

This work proposes a language for describing reactive synthesis problems that integrates imperative and declarative elements. The semantics is defined in terms of two-player turn-based infinite games with full information. Currently, synthesis tools accept linear temporal logic (LTL) as input, but this description is less structured and does not facilitate the expression of sequential constraints. This motivates the use of a structured programming language to specify synthesis problems. Transition systems and guarded commands serve as imperative constructs, expressed in a syntax based on that of the modeling language Promela. The syntax allows defining which player controls data and control flow, and separating a program into assumptions and guarantees. These notions are necessary for input to game solvers. The integration of imperative and declarative paradigms allows using the paradigm that is most appropriate for expressing each requirement. The declarative part is expressed in the LTL fragment of generalized reactivity(1), which admits efficient synthesis algorithms. The implementation translates Promela to input for the Slugs synthesizer and is written in Python