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 proceedings of the 24th International Conference on Implementation and Application of Automata, CIAA 2019, held in Kosice, Slovakia, in July 2019.The 17 regular papers presented together with 2 invited papers in this book were carefully reviewed and selected from 29 initial submissions. The topics of the papers include complexity of languages and language operations, regular expressions, picture languages, jumping automata, input driven and two-dimensional automata, tree languages and tree transducers, architecture of oritatami systems, intruder deduction problem, context sensitive ash codes, rational relations, and algorithms for manipulating sequence binary decision diagrams

This book constitutes the proceedings of the 22nd International Conference on Descriptional Complexity of Format Systems, DCFS 2020, which was supposed to take place in Vienna, Austria, in August 2020, but the conference was canceled due to the COVID-19 crisis.The 19 full papers presented in this volume were carefully reviewed and selected from 31 submissions. 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.