Generalising submodularity and horn clauses: Tractable optimization problems defined by tournament pair multimorphisms

Submodularity and Horn Clauses : Tractable Optimization Problems Defined Bytournament Pair

Generalising tractable VCSPs defined by symmetric tournament pair multimorphisms

We study optimisation problems that can be formulated as valued constraint satisfaction problems (VCSP). A problem from VCSP is characterised by a constraint language, a fixed set of cost functions taking finite and infinite costs over a finite domain. An instance of the problem is specified by a sum of cost functions from the language and the goal is to minimise the sum. We are interested in t...

Solving Constrained Horn Clauses Using Dependence-Disjoint Expansions

Recursion-free Constrained Horn Clauses (CHCs) are logicprogramming problems that formulate verifying safety of programs with bounded iteration and recursion. They both formulate bounded verification problems and are generated by solvers that attempt to verify safety of unbounded iterative or recursive systems. Efficient solvers of recursion-free systems reduce the problem to solving a series o...

Cryptographic Protocol Verification Using Tractable Classes of Horn Clauses

We consider secrecy problems for cryptographic protocols modeled using Horn clauses and present general classes of Horn clauses which can be efficiently decided. Besides simplifying the methods for the class of flat and onevariable clauses introduced for modeling of protocols with single blind copying [7,25], we also generalize this class by considering k-variable clauses instead of one-variabl...

The complexity of soft constraint satisfaction

Over the past few years there has been considerable progress in methods to systematically analyse the complexity of constraint satisfaction problems with specified constraint types. One very powerful theoretical development in this area links the complexity of a set of constraints to a corresponding set of algebraic operations, known as polymorphisms. In this paper we extend the analysis of com...