This permits dealing with operational and denotational issues within the same model theory and logic. A programming language called Maude whose modules are rewriting logic theories is defined and given denotational and operational semantics. Maude provides a simple unification of concurrent programming with functional and object-oriented programming and supports high level declarative programming of concurrent systems.

Equational logic appears as a special refinement of the general framework; this supports a natural unification of the functional and concurrent programming paradigms with a purely declarative style. Throughout the paper, the concurrent nature of term rewriting is emphasized; the role of rewriting as a unified model of concurrency is also discussed.

This Festschrift volume contains 28 refereed papers including personal memories, essays, and regular research papers by close collaborators and friends of José Meseguer to honor him on the occasion of his 65th birthday. These papers were presented at a symposium at the University of Illinois at Urbana-Champaign on September 23-25, 2015. The symposium also featured invited talks by Claude and Hélène Kirchner and by Patrick Lincoln. The foreword of this volume adds a brief overview of some of José's many scientific achievements followed by a bibliography of papers written by José.

This volume contains the proceedings of the Eighth International Workshop on Rewriting Logic and its Applications (WRLA 2010) that was held in Paphos, Cyprus, March 20–21, 2010, as a satellite workshop of the European Joint C- ferences on Theory and Practice of Software (ETAPS 2010). Rewriting logic is a natural semantic framework for representing conc- rency,parallelism,communicationandinteraction,aswellasbeing anexpressive (meta)logical framework for representing logics. It can then be used for spe- fying a wide range of systems and programming languages in various appli- tion ?elds. In recent years, several executable speci?cation languages based on rewriting logic (ASF+SDF, CafeOBJ, ELAN, Maude) have been designed and implemented. The aim of the WRLA workshop series is to bring together - searchers with a common interest in rewriting logic and its applications, and to give them the opportunity to present their recent works, discuss future research directions, and exchange ideas. Previous WRLA workshops were held in Asilomar (1996), Pont-a-Mousson ` (1998), Kanazawa (2000), Pisa (2002), Barcelona (2004), Vienna (2006), and Budapest (2008), and their proceedings have been published inElectronic Notes in Theoretical Computer Science. In addition, selected papers from WRLA 1996 have been published in a special issue of Theoretical Computer Science,and selected papers from WRLA 2004 appeared in a special issue of Higher-Order and Symbolic Computation.

In recent years, extensions of rewriting techniques that go beyond the traditional untyped algebraic rewriting framework have been investigated and developed. Among these extensions, conditional and typed systems are particularly important, as are higher-order systems, graph rewriting systems, etc. The international CTRS (Conditional and Typed Rewriting Systems) workshops are intended to offer a forum for researchers on such extensions of rewriting techniques. This volume presents the proceedings of the second CTRS workshop, which contributed to discussion and evaluation of new directions of research. (The proceedings of the first CTRS workshop are in Lecture Notes in Computer Science, Vol. 308.) Several important directions for extensions of rewriting techniques were stressed, which are reflected in the organization of the chapters in this volume: - Theory of conditional and Horn clause systems, - Infinite terms, non-terminating systems, and termination, - Extension of Knuth-Bendix completion, - Combined systems, combined languages and modularity, - Architecture, compilers and parallel computation, - Basic frameworks for typed and order-sorted systems, - Extension of unification and narrowing techniques.

This book constitutes the refereed proceedings of the 16th International Conference on Concurreny Theory, CONCUR 2005, held in San Francisco, CA, USA in August 2005. The 38 revised full papers presented together with 4 invited papers were carefully reviewed and selected from 100 submissions. Among the topics covered are concurrency related aspects of models of computation, Petri nets, model checking, game semantics, process algebras, real-time systems, verification techniques, secrecy and authenticity, refinement, distributed programming, constraint logic programming, typing systems and algorithms, case studies, tools, and environment for programming and verification.

th FM 2009, the 16 International Symposium on Formal Methods, marked the 10th an- versary of the First World Congress on Formal Methods that was held in 1999 in Toulouse, France. We wished to celebrate this by advertising and organizing FM 2009 as the Second World Congress in the FM series, aiming to once again bring together the formal methods communities from all over the world. The statistics displayed in the table on the next page include the number of countries represented by the Programme Committee members, as well as of the authors of submitted and accepted papers. Novel this year was a special track on tools and industrial applications. Subm- sions of papers on these topics were especially encouraged, but not given any special treatment. (It was just as hard to get a special track paper accepted as any other paper.) What we did promote, however, was a discussion of how originality, contri- tion, and soundness should be judged for these papers. The following questions were used by our Programme Committee.