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Developments in Language Theory 21st International Conference, DLT 2017, Liège, Belgium, August 711, 2017, Proceedings
The 21st International Conference on Developments in Language Theory (DLT 2017) was organized by the Department of Mathematics of the University of Liège, Belgium, during August 7–11, 2017.
The DLT conference series is one of the major international conference series in language theory and related areas. The DLT conference was established by G. Rozenberg and A. Salomaa in 1993. Since then, the DLT conferences have been held on every odd year: Magdeburg, Germany (1995), Thessaloniki, Greece (1997), Aachen, Germany (1999), and Vienna, Austria (2001). Since 2001, a DLT conference has been taking place in Europe on every odd year and outside Europe on every even year. The locations of DLT conferences since 2002 were: Kyoto, Japan (2002), Szeged, Hungary (2003), Auckland, New Zealand (2004), Palermo, Italy (2005), Santa Barbara, California, USA (2006), Turku, Finland (2007), Kyoto, Japan (2008), Stuttgart, Ger many (2009), London, Ontario, Canada (2010), Milan, Italy (2011), Taipei, Taiwan (2012), MarnelaVallée, France (2013), Ekaterinburg, Russia (2014), Liverpool, UK (2015), and Montréal, Canada (2016). This 21st edition was thus the first time that the conference was organized in Belgium.
The series of International Conferences on Developments in Language Theory provides a forum for presenting current developments in formal languages and auto mata. Its scope is very general and includes, among others, the following topics and areas: combinatorial and algebraic properties of words and languages; grammars, acceptors and transducers for strings, trees, graphs, arrays; algebraic theories for automata and languages; codes; efficient text algorithms; symbolic dynamics; decision problems; relationships to complexity theory and logic; picture description and anal ysis; polyominoes and bidimensional patterns; cryptography; concurrency; cellular automata; bioinspired computing; quantum computing.
The papers submitted to DLT 2017 were from 19 countries including Belgium, Canada, Czech Republic, France, Germany, Hungary, India, Italy, Japan, The Netherlands, Poland, Portugal, Republic of Korea, Russia, Slovakia, South Africa, Thailand, and USA.
This volume of Lecture Notes in Computer Science contains the papers that were presented at DLT 2017. There were 47 qualified submissions. Each submission was handled by three Program Committee members and received at least three reviews. The committee decided to accept 24 papers. The volume also includes the abstracts or full papers of the invited speakers:

– Véronique Bruyère (University of Mons): “ComputerAided Synthesis: A GameTheoretic Approach”

– Sergei Kitaev (University of Strathclyde): “A Comprehensive Introduction to the Theory of WordRepresentable Graphs”

– Robert Mercaş (Loughborough University): “On the Number of Factors with MaximalExponent in Words”

– Balasubramanian Ravikumar (Sonoma State University): “Language Approxima tion: Asymptotic and Nonasymptotic Results”

– Eric Rowland (Hofstra University): “Binomial Coefficients, Valuations, and Words”

– Michał‚ Skrzypczak (University of Warsaw): “Connecting Decidability and Com plexity for MSO Logic”
We warmly thank all the invited speakers and all the authors of the submitted papers. We also would like to thank all the members of the Program Committee and all the external reviewers (listed in the proceedings) for their excellent work in evaluating the papers. We finally thank all the members of the Organizing Committee at the University of Liège.
The organization of the conference benefited from the support of the F.R.S.FNRS, the Faculty of Sciences of the University of Liège and the Research Unit in Mathe matics of the University of Liège. The reviewing process was organized using the EasyChair conference system created by Andrei Voronkov. We would like to acknowledge that this system greatly helped to improve the efficiency of the committee work. Finally, we wish to thank the editors of the Lecture Notes in Computer Science series and Springer.
May 2017
Émilie Charlier Julien Leroy Michel Rigo