Invited Papers -- Well-Founded and Partial Stable Semantics Logical Aspects -- The Reachability Problem over Infinite Graphs -- Kolmogorov Complexity and Model Selection -- Automatic Verification of Heap-Manipulating Programs Using Separation Logic -- Accepted Papers -- Canonical Calculi: Invertibility, Axiom Expansion and (Non)-determinism -- Integrality Property in Preemptive Parallel Machine Scheduling -- Characterizing the Existence of Optimal Proof Systems and Complete Sets for Promise Classes -- k-SAT Is No Harder Than Decision-Unique-k-SAT -- Unique Decipherability in the Monoid of Languages: An Application of Rational Relations -- Concurrently Non-malleable Black-Box Zero Knowledge in the Bare Public-Key Model -- Approximability Distance in the Space of H-Colourability Problems -- On Random Ordering Constraints -- Depth Reduction for Circuits with a Single Layer of Modular Counting Gates -- A Feebly Secure Trapdoor Function -- Partitioning Graphs into Connected Parts -- Structural Complexity of AvgBPP -- Lower Bounds for the Determinantal Complexity of Explicit Low Degree Polynomials -- Simulation of Arithmetical Circuits by Branching Programs with Preservation of Constant Width and Syntactic Multilinearity -- One-Nonterminal Conjunctive Grammars over a Unary Alphabet -- Concatenation of Regular Languages and Descriptional Complexity -- Approximability of the Maximum Solution Problem for Certain Families of Algebras -- Complete Complexity Classification of Short Shop Scheduling -- Compressed Word Problems in HNN-Extensions and Amalgamated Products -- Variations on Muchnik’s Conditional Complexity Theorem -- An Optimal Bloom Filter Replacement Based on Matrix Solving -- Aperiodicity Measure for Infinite Sequences -- On the Complexity of Matroid Isomorphism Problems -- Breaking Anonymity by Learning a Unique Minimum Hitting Set -- The Budgeted Unique Coverage Problem and Color-Coding -- Formal Verification of Gate-Level Computer Systems -- On Models of a Nondeterministic Computation -- New Plain-Exponential Time Classes for Graph Homomorphism -- Languages Recognized with Unbounded Error by Quantum Finite Automata.

This book constitutes the refereed proceedings of the Fourth International Computer Science Symposium in Russia, CSR 2009, held in Novosibirsk, Russia, August 18-23, 2009. The 29 revised papers presented together with 4 invited papers were carefully reviewed and selected from 66 submissions. All major areas in computer science are addressed. The theory track deals with algorithms, protocols, and data structures; complexity and cryptography; formal languages, automata and their applications to computer science; computational models and concepts; proof theory and applications of logic to computer science.