Structuring and modularizing algebraic specifications: the PLUSS specification language, evolutions and perspectives -- The parallel complexity of tree embedding problems (extended abstract) -- A theory of strict P-completeness -- Fast and optimal simulations between CRCW PRAMs -- Suitability of the propositional temporal logic to express properties of real-time systems -- Axiomatizations of backtracking -- Joining k- and l-recognizable sets of natural numbers -- On the performance of networks with multiple busses -- Efficient algorithms for solving systems of linear equations and path problems -- Efficient sublinear time parallel algorithms for dynamic programming and context-free recognition -- A simplified technique for hidden-line elimination in terrains -- A competitive analysis of nearest neighbor based algorithms for searching unknown scenes -- Equality and disequality constraints on direct subterms in tree automata -- Deterministic regular languages -- The extended low hierarchy is an infinite hierarchy -- Locally definable acceptance types for polynomial time machines -- The theory of the polynomial many-one degrees of recursive sets is undecidable -- A plane-sweep algorithm for finding a closest pair among convex planar objects -- Linear approximation of simple objects -- Language learning without overgeneralization -- The log-star revolution -- Separating counting communication complexity classes -- A nonlinear lower bound on the practical combinational complexity -- Characterizations of some complexity classes between ? 2 p and ? 2 p -- On complexity classes and algorithmically random languages -- New time hierarchy results for deterministic TMS -- Unconditional Byzantine agreement for any number of faulty processors -- Broadcasting in butterfly and debruijn networks -- Interval approximations of message causality in distributed executions -- On the approximability of the maximum common subgraph problem -- The complexity of colouring circle graphs -- Graph isomorphism is low for PP -- A simple linear time algorithm for triangulating three-colored graphs -- On locally optimal alignments in genetic sequences -- Secure commitment against a powerful adversary -- Communication efficient Zero-knowledge Proofs of knowledge -- Four results on randomized incremental constructions -- Enclosing many boxes by an optimal pair of boxes -- Performance driven k-layer wiring -- Synthesis for testability: Binary Decision Diagrams -- Compression and entropy -- Iterative devices generating infinite words -- On the factorization conjecture -- Conditional semi-Thue systems for presenting monoids -- A combinatorial bound for linear programming and related problems -- In-place linear probing sort -- Speeding up two string-matching algorithms -- The ANIGRAF system -- A programming language for symbolic computation of regular languages, automata and semigroups -- ?SPEED: a system for the specification and verification of microprocessors -- A discrete event simulator of communication algorithms in interconnection networks -- ALPHA DU CENTAUR: An environment for the design of systolic arrays -- Verification of communicating processes by means of automata reduction and abstraction -- Distributed system simulator (DSS) -- An interactive proof tool for process algebras -- SPECI90 A term rewriting and narrowing system.

This volume gives the proceedings of the ninth Symposium on Theoretical Aspects of Computer Science (STACS). This annual symposium is held alternately in France and Germany and is organized jointly by the Special Interest Group for Fundamental Computer Science of the Association Francaise des Sciences et Technologies de l'Information et des Syst mes (AFCET) and the Special Interest Group for Theoretical Computer Science of the Gesellschaft f}r Informatik (GI). The volume includes three invited lectures and sections on parallel algorithms, logic and semantics, computational geometry, automata and languages, structural complexity, computational geometry and learning theory, complexity and communication, distributed systems, complexity, algorithms, cryptography, VLSI, words and rewriting, and systems.