This book constitutes the proceedings of the 21st International Conference on Descriptional Complexity of Format Systems, DCFS 2019, held in Kosice, Slovakia, in July 2019. The 18 full papers presented in this volume were carefully reviewed and selected from 25 submissions. The book also contains 4 invited talks. They deal with all aspects of descriptional complexity and costs of description of objects in various computational models, such as Turing machines, pushdown automata, finite automata, grammars, and others.

This book constitutes the thoroughly refereed papers of the 18th International Conference on Implementation and Application of Automata, CIAA 2013, held in Halifax, NS, Canada, in July 2013. The 25 revised full papers presented together with 3 invited papers and 7 short papers were carefully selected from 43 submissions. The papers cover various topics such as complexity of automata; compressed automata; counter automata; dictionary matching; edit distance; homing sequences; implementation; minimization of automata; model checking; parsing of regular expressions; partial word automata; picture languages; pushdown automata; queue automata; reachability analysis for software verification; restarting automata; transducers; tree automata; weighted automata; XML streams.

This book constitutes the proceedings of the 20th International Conference on Descriptional Complexity of Formal Systems, DCFS 2018, held in Halifax, NS, Canada, in July 2018. The 19 full papers presented were carefully reviewed and selected from 24 submissions. DCFS is an annual international working conference concerning the descriptional complexity of formal systems and structures and its applications. Topics of interest are related to all aspects of descriptional complexity and much more.

This volume brings together the work of several prominent researchers who have collaborated with Janusz Brzozowski, or worked in topics he developed, in the areas of regular languages, syntactic semigroups of formal languages, the dot-depth hierarchy, and formal modeling of circuit testing and software specification using automata theory.