This volume contains the proceedings of FroCoS 2002, the 4th International Workshop on Frontiers of Combining Systems, held April 8-10, 2002 in Santa Margherita Ligure (near Genova), Italy. Like its predecessors, organized in - nich (1996), Amsterdam (1998), and Nancy (2000), FroCoS 2002 o?ered a c- mon forum for the presentation and discussion of research activities on the c- bination and integration of systems in various areas of computer science, such as logic, computation, program development and proof, arti?cial intelligence, mechanical veri?cation, and symbolic computation. There were 35 submissions of high quality, authored by researchers from countries including Australia, Belgium, Brazil, Finland, France, Germany, Italy, Portugal, Spain, Singapore, United Kingdom, United States of America, and - goslavia. All the submissions were thoroughly evaluated on the basis of at least three referee reports, and an electronic program committee meeting was held through the Internet. The program committee selected 14 research contributions. The topics covered by the selected papers include: combination of logics, c- bination of constraint solving techniques, combination of decision procedures, combination problems in veri?cation, modular properties of theorem proving, integration of decision procedures and other solving processes into constraint programming and deduction systems.

Foundations of a Constraint-Based Illustrator.- Integrating HOL-CASL into the Development Graph Manager MAYA.- Monads and Modularity.- A Modular Approach to Proving Confluence.- Integrating BDD-Based and SAT-Based Symbolic Model Checking.- Heuristics for Efficient Manipulation of Composite Constraints.- Constraint-Based Model Checking for Parameterized Synchronous Systems.- A Rewrite Rule Based Framework for Combining Decision Procedures *.- Combining Sets with Integers.- Solving Nonlinear Equations by Abstraction, Gaussian Elimination, and Interval Methods.- A Generalization of Shostak#x2019;s Method for Combining Decision Procedures.- Combining Relational Algebra, SQL, and Constraint Programming.- Computational Complexity of Propositional Linear Temporal Logics Based on Qualitative Spatial or Temporal Reasoning.- Exploiting Constraints for Domain Managing in CLP(FD).- Tutorial: Reasoning with, about and for Constraint Handling Rules.- PROSPER An Investigation into Software Architecture for Embedded Proof Engines.- Constraint-Lambda Calculi.- Labelled Deduction over Algebras of Truth-Values*.- A Temporal × Modal Approach to the Definability of Properties of Functions.