Invited Papers -- When Worlds Collide: Derandomization, Lower Bounds, and Kolmogorov Complexity -- Approximation Schemes for Geometric NP-Hard Problems: A Survey -- On Clustering Using Random Walks -- An Introduction to Decidability of DPDA Equivalence -- Semidefinite Programming Based Approximation Algorithms -- Contributed Papers -- Hard Sets and Pseudo-random Generators for Constant Depth Circuits -- The First-Order Isomorphism Theorem -- Thresholds and Optimal Binary Comparison Search Trees -- Distributed LTL Model Checking Based on Negative Cycle Detection -- Computability and Complexity Results for a Spatial Assertion Language for Data Structures -- Using Nondeterminism to Design Efficient Deterministic Algorithms -- Liveness Verification of Reversal-Bounded Multicounter Machines with a Free Counter -- A Mechanically Verified Compiling Specification for a Lisp Compiler -- Beyond Regular Model Checking -- Relations Between Communication Complexity, Linear Arrangements, and Computational Complexity -- Optimal, Output-Sensitive Algorithms for Constructing Upper Envelope of Line Segments in Parallel -- List Decoding from Erasures: Bounds and Code Constructions -- Verification of a Leader Election Algorithm in Timed Asynchronous Systems -- Efficient Addition on Field Programmable Gate Arrays -- The Directed Minimum-Degree Spanning Tree Problem -- I/O-Efficient Batched Range Counting and Its Applications to Proximity Problems -- Beyond Message Sequence Graphs -- Grouping Techniques for One Machine Scheduling Subject to Precedence Constraints -- Properties of Distributed Timed-Arc Petri Nets -- From Falsification to Verification -- On Polynomial Representations of Boolean Functions Related to Some Number Theoretic Problems -- Range Allocation for Equivalence Logic -- Rewrite Closure for Ground and Cancellative AC Theories.

This volume contains the proceedings of the 21st international conference on the Foundations of Software Technology and Theoretical Computer Science (FSTTCS 2001), organized under the auspices of the Indian Association for Research in Computing Science (IARCS). This year’s conference attracted 73 submissions from 20 countries. Each s- mission was reviewed by at least three independent referees. In a departure from previous conferences, the ?nal selection of the papers making up the program was done through an electronic discussion spanning two weeks, without a physical meeting of the Program Committee (PC). Since the PC of FSTTCS is distributed across the globe, it is very di?cult to ?x a meeting whose time and venue is convenient for a substantial fraction of the PC. Given this, it was felt that an electronic discussion would enable all members to participate on a more equal footing in the ?nal selection. All reviews, scores, and comments were posted on a secure website, with a mechanism for making updates and automatically sending noti?cations by email to relevant members of the PC. All PC members participated actively in the discussion. The general feedback on the arrangement was very positive, so we hope to continue this in future years. We had ?ve invited speakers this year: Eric Allender, Sanjeev Arora, David Harel, Colin Stirling, and Uri Zwick. We thank them for having readily accepted our invitation to talk at the conference and for providing abstracts (and even full papers) for the proceedings.