Section 1. Invited Contributions.- Architecting Solvers for SAT Modulo Theories: Nelson-Oppen with DPLL.- From KSAT to Delayed Theory Combination: Exploiting DPLL Outside the SAT Domain.- Hierarchical and Modular Reasoning in Complex Theories: The Case of Local Theory Extensions.- Temporalising Logics: Fifteen Years After.- Section 2. Technical Papers.- Termination of Innermost Context-Sensitive Rewriting Using Dependency Pairs.- A Compressing Translation from Propositional Resolution to Natural Deduction.- Combining Algorithms for Deciding Knowledge in Security Protocols.- Combining Classical and Intuitionistic Implications.- Towards an Automatic Analysis of Web Service Security.- Certification of Automated Termination Proofs.- Temporal Logic with Capacity Constraints.- Idempotent Transductions for Modal Logics.- A Temporal Logic of Robustness.- Noetherianity and Combination Problems.- Languages Modulo Normalization.- Combining Proof-Producing Decision Procedures.- Visibly Pushdown Languages and Term Rewriting.- Proving Termination Using Recursive Path Orders and SAT Solving.

This book constitutes the refereed proceedings of the 6th International Symposium on Frontiers of Combining Systems, FroCoS 2007, held in Liverpool, UK, September 2007. The 14 revised full papers presented were carefully selected and are organized in topical sections on combinations of logics, theories, and decision procedures; constraint solving and programming; combination issues in rewriting and programming as well as in logical frameworks and theorem proving systems.