Descriptional Complexity of Formal Systems 21st IFIP WG 1.02 International Conference, DCFS 2019, Košice, Slovakia, July 17-19, 2019, Proceedings - Hospodár, Michal; Hospodár, Michal; Jirásková, Galina; Jirásková, Galina; Konstantinidis, Stavros; Konstantinidis, Stavros (Springer International Publishing : Imprint: Springer, 2019)