This volume contains the proceedings of CONCUR '93, thefourth in an annual series of conferences devoted to thestudy of concurrency. Bergstra, "Loop parallelization in thepolytope model" by Christian Lengauer, and "Structuredoperational semantics for process algebras and equationalaxiom systems" (abstract) by Bard Bloom.

The lambda-calculus with multiplicities.- A multiset semantics for the pi-calculus with replication.- Model checking mobile processes.- A practical technique for process abstraction.- Modular completeness for Communication Closed Layers.- The linear time — Branching time spectrum II.- A classification of models for concurrency.- On the ill-timed but well-caused.- On the reduction of chocs bisimulation to ?-calculus bisimulation.- A theory of bisimulation for the ?-calculus.- Bisimulation equivalence is decidable for basic parallel processes.- A pi-calculus semantics for an object-based design notation.- Programming with broadcasts.- Interpreting broadcast communication in SCCS.- Proof systems for message-passing process algebras.- Refinement and decomposition of value-passing action systems.- Partial-order methods for temporal verification.- Model construction for implicit specifications in modal logic.- Branching time temporal logic and amorphous tree automata.- A generalized event structure for the Muller unfolding of a safe net.- Domains of higher-dimensional automata.- Non interleaving process algebra.- Quiescence, fairness, testing, and the notion of implementation.- Two fully abstract models for UNITY.- Transformations preserving properties and properties preserved by transformations in fair transition systems (extended abstract).- Minimal memory schedules for dataflow networks.- Networks of real-time processes.- Loop parallelization in the polytope model.- ACSR: An algebra of communicating shared resources with dense time and priorities.- An Elimination Theorem for regular behaviours with integration.- A linear local model checking algorithm for CTL.- Local event structures and Petri nets.- A congruence theorem for structured operational semantics withpredicates.- From CML to process algebras.- Types for dyadic interaction.- Principal typing schemes in a polyadic ?-calculus.- Structured operational semantics for process algebras and equational axiom systems.