Dedicated to Andrzej Ehrenfeucht on the occasion of his 65th birthday, the essays in this volume centre around Ehrenfeucht's scientific work. The book is organized in topical sections on model theory, games and logic, graphs and algorithms, pattern matching and learning, and combinatorics of word.

On the work of Andrzej Ehrenfeucht in model theory.- Syntax vs. semantics on finite structures.- Expressive power of unary counters.- Some strange quantifiers.- Pebble games in model theory.- An interpretive isomorphism between binary and ternary relations.- Vagueness — A rough set view.- Ehrenfeucht games, the composition method, and the monadic theory of ordinal words.- Monadic second order logic and node relations on graphs and trees.- Approximating the volume of general Pfaffian bodies.- Complement-equivalence classes on graphs.- On compact directed acyclic word graphs.- Metric entropy and minimax risk in classification.- Of periods, quasiperiods, repetitions and covers.- Combinatorics of standard Sturmian words.- Compactness of systems of equations on completely regular semigroups.- Decision problems concerning algebraic series with noncommuting variables.- Associative shuffle of infinite words.- Constructing sequential bijections.- Rewriting rules for synchronization languages.- DNA sequence classification using DAWGs.- DNA computing: Distributed splicing systems.