Lazy Kleene Algebra

We propose a relaxation of Kleene algebra by giving up strictness and right-distributivity of composition. This allows the subsumption of Dijkstra's computation calculus, Cohen's omega algebra and von Wright's demonic refinement algebra. Moreover, by adding domain and codomain operators we can also incorporate modal operators. Finally, it is shown that the predicate transformers form lazy Kleene algebras again, the disjunctive and conjunctive ones even lazy Kleene algebras with an omega operation

Algebraic Principles for Rely-Guarantee Style Concurrency Verification Tools

We provide simple equational principles for deriving rely-guarantee-style inference rules and refinement laws based on idempotent semirings. We link the algebraic layer with concrete models of programs based on languages and execution traces. We have implemented the approach in Isabelle/HOL as a lightweight concurrency verification tool that supports reasoning about the control and data flow of concurrent programs with shared variables at different levels of abstraction. This is illustrated on two simple verification examples

Epistemic Semantics in Guarded String Models

Constructive and computable multi-agent epistemic possible worlds models are interpreted as sets of guarded string models in an epistemic extension of Kleene Algebra with Tests (KAT}). The account is framed as a formal language EpiKAT (Epistemic KAT) for defining such models. The language is implemented by translation into the finite state calculus, and alternatively by modeling propositions as lazy lists in Haskell. The syntax-semantics interface for a fragment of English is defined by a categorial grammar

Refinement algebra for probabilistic programs

We identify a refinement algebra for reasoning about probabilistic program transformations in a total-correctness setting. The algebra is equipped with operators that determine whether a program is enabled or terminates respectively. As well as developing the basic theory of the algebra we demonstrate how it may be used to explain key differences and similarities between standard (i.e. non-probabilistic) and probabilistic programs and verify important transformation theorems for probabilistic action systems.29 page(s

Non-smooth and zeno trajectories for hybrid system algebra

Hybrid systems are heterogeneous systems characterised by the interaction of discrete and continuous dynamics. In this paper we compare a slightly extended version of our earlier algebraic approach to hybrid systems with other approaches. We show that hybrid automata, which are probably the standard tool for describing hybrid systems, can conveniently be embedded into our algebra. But we allow general transition functions, not only smooth ones. Moreover we embed other models and point out some important advantages of the algebraic approach. In particular, we show how to easily handle Zeno effects, which are excluded by most other authors. The development of the theory is illustrated by a running example and a larger case study