See my publications by year or at ORCID, Google Scholar, DBLP, ACM DL, and arXiv.org.
A list of published (extended) abstracts is available here.

PhD Thesis

• Thomas Vogel. Model-Driven Engineering of Self-Adaptive Software. PhD Thesis, University of Potsdam, Germany, 2018.

Edited Publications

• Iris Groher and Thomas Vogel, eds. Joint Proceedings of the Software Engineering 2023 Workshops. Digital Library of the Gesellschaft für Informatik (GI), 2023.
• Holger Schlingloff, Andrzej Skowron, and Thomas Vogel, eds. Concurrency, Specification and Programming – Revised Selected Papers from the 29th International Workshop on Concurrency, Specification and Programming (CS&P’21), Berlin, Germany. Series: Studies in Computational Intelligence. Springer Cham, 2023.
• Holger Schlingloff and Thomas Vogel, eds. Proceedings of the 29th International Workshop on Concurrency, Specification and Programming (CS&P 2021). Vol. 2951. CEUR-WS.org. 2021.
• Joel Greenyer, Malte Lochau, and Thomas Vogel, eds. Explainable Software for Cyber-Physical Systems (ES4CPS): Report from the GI Dagstuhl Seminar 19023, January 06-11 2019, Schloss Dagstuhl. arXiv:1904.11851. 2019.
• Simos Gerasimou, Thomas Vogel, and Ada Diaconescu, eds. Software Engineering for Intelligent and Autonomous Systems: Report from the GI Dagstuhl Seminar 18343. arXiv:1904.01518. 2019.
• Thomas Vogel, Matthias Tichy, and Alessandra Gorla, eds. Report from the GI Dagstuhl Seminar 14433: Software Engineering for Self-Adaptive Systems. Research Reports in Software Engineering and Management 2014:02. Department of Computer Science, Engineering, Chalmers University of Technology, and University of Gothenburg, Sweden. 2014.

Journals

• Arut Prakash Kaleeswaran, Arne Nordmann, Thomas Vogel, and Lars Grunske. A User Study for Evaluation of Formal Verification Results and their Explanation at Bosch. In: Empirical Software Engineering (EMSE) 28.125 (2023).
• Thomas Vogel, Marc Carwehl, Genaína Nunes Rodrigues, and Lars Grunske. A Property Specification Pattern Catalog for Real-Time System Verification with UPPAAL. In: Information and Software Technology 154 (2023), p. 107100. (Available online 01 November 2022).
• Arut Prakash Kaleeswaran, Arne Nordmann, Thomas Vogel, and Lars Grunske. A Systematic Literature Review on Counterexample Explanation. In: Information and Software Technology 145 (2022), p. 106800. (Available online 30 December 2021).
• Laura Wartschinski, Yannic Noller, Thomas Vogel, Timo Kehrer, and Lars Grunske. Vudenc: Vulnerability Detection with Deep Learning on a Natural Codebase for Python. In: Information and Software Technology 144 (2022), p. 106809. (Available online 01 January 2022).
• Danny Weyns, Ilias Gerostathopoulos, Barbora Buhnova, Nicolás Cardozo, Emilia Cioroaica, Ivana Dusparic, Lars Grunske, Pooyan Jamshidi, Christine Julien, Judith Michael, Gabriel Moreno, Shiva Nejati, Patrizio Pelliccione, Federico Quin, Genaina Rodrigues, Bradley Schmerl, Marco Vieira, Thomas Vogel, and Rebekka Wohlrab. Guidelines for Artifacts to Support Industry-Relevant Research on Self-Adaptation. In: SIGSOFT Softw. Eng. Notes 47.4 (2022), pp. 18–24.
• Thomas Vogel, Chinh Tran, and Lars Grunske. A Comprehensive Empirical Evaluation of Generating Test Suites for Mobile Applications with Diversity. In: Information and Software Technology 130 (2021), p. 106436. (Available online 25 September 2020).
• Sona Ghahremani, Holger Giese, and Thomas Vogel. Improving Scalability and Reward of Utility-Driven Self-Healing for Large Dynamic Architectures. In: ACM Transactions on Autonomous and Adaptive Systems 14.3 (2020), 12:1–12:41.
• Antonio Filieri, Martina Maggio, Konstantinos Angelopoulos, Nicolás D’ippolito, Ilias Gerostathopoulos, Andreas Berndt Hempel, Henry Hoffmann, Pooyan Jamshidi, Evangelia Kalyvianaki, Cristian Klein, Filip Krikava, Sasa Misailovic, Alessandro V. Papadopoulos, Suprio Ray, Amir M. Sharifloo, Stepan Shevtsov, Mateusz Ujma, and Thomas Vogel. Control Strategies for Self-Adaptive Software Systems. In: ACM Transactions on Autonomous and Adaptive Systems 11.4 (2017), 24:1–24:31.
• Thomas Vogel and Holger Giese. Model-Driven Engineering of Self-Adaptive Software with EUREMA. In: ACM Transactions on Autonomous and Adaptive Systems 8.4 (2014), 18:1–18:33.

Conferences

• Marc Carwehl, Thomas Vogel, Genaína Nunes Rodrigues, and Lars Grunske. Runtime Verification of Self-Adaptive Systems with Changing Requirements. In: 18th International Symposium on Software Engineering for Adaptive and Self-Managing Systems. SEAMS ’23. IEEE, 2023, pp. 104–114.
• Danny Weyns and Thomas Vogel. On the Need for Artifacts to Support Research on Self-Adaptation Mature for Industrial Adoption. In: 18th International Symposium on Software Engineering for Adaptive and Self-Managing Systems. SEAMS ’23. IEEE, 2023, pp. 86–87.
• Ilias Gerostathopoulos, Thomas Vogel, Danny Weyns, and Patricia Lago. How do we Evaluate Self-adaptive Software Systems? In: 16th International Symposium on Software Engineering for Adaptive and Self-Managing Systems. SEAMS ‘21. IEEE, 2021, pp. 59–70.
• Arut Prakash Kaleeswaran, Arne Nordmann, Thomas Vogel, and Lars Grunske. A User-Study Protocol for Evaluation of Formal Verification Results and their Explanation. In: Registered Reports Track at the 37th International Conference on Software Maintenance and Evolution (ICSME). ICSME RR ‘21. 2021.
• Ricardo D. Caldas, Arthur Rodrigues, Eric B. Gil, Genaína N. Rodrigues, Thomas Vogel, and Patrizio Pelliccione. A Hybrid Approach Combining Control Theory and AI for Engineering Self-Adaptive Systems. In: 15th International Symposium on Software Engineering for Adaptive and Self-Managing Systems. SEAMS ’20. ACM, 2020, pp. 9–19.
• Javier Cámara, Alessandro V. Papadopoulos, Thomas Vogel, Danny Weyns, David Garlan, Shihong Huang, and Kenji Tei. Towards Bridging the Gap between Control and Self-Adaptive System Properties. In: 15th International Symposium on Software Engineering for Adaptive and Self-Managing Systems. SEAMS ’20. ACM, 2020, pp. 78–84.
• Martin Eberlein, Yannic Noller, Thomas Vogel, and Lars Grunske. Evolutionary Grammar-Based Fuzzing. In: 12th Symposium on Search-Based Software Engineering. SSBSE ‘20. Springer, 2020, pp. 105–120.
• Sebastian Müller, Thomas Vogel, and Lars Grunske. Bet and Run for Test Case Generation. In: 12th Symposium on Search-Based Software Engineering. SSBSE ‘20. Springer, 2020, pp. 204–219.
• Arut Prakash Kaleeswaran, Arne Nordmann, Thomas Vogel, and Lars Grunske. Counterexample Interpretation for Contract-Based Design. In: 7th International Symposium on Model-Based Safety and Assessment. IMBSA ’20. Springer, 2020, pp. 99–114.
• Thomas Vogel, Chinh Tran, and Lars Grunske. Does Diversity Improve the Test Suite Generation for Mobile Applications?. In: 11th International Symposium on Search-Based Software Engineering. SSBSE ‘19. LNCS 11664. Springer, 2019, pp. 58–74.
• Erik Fredericks, Ilias Gerostathopoulos, Christian Krupitzer, and Thomas Vogel. Planning as Optimization: Dynamically Discovering Optimal Configurations for Runtime Situations. In: International Conference on Self-Adaptive and Self-Organizing Systems. SASO ‘19. IEEE, 2019, pp. 1–10.
• Gabriela Solano, Ricardo Caldas, Genaina Rodrigues, Thomas Vogel, and Patrizio Pelliccione. Taming Uncertainty in the Assurance Process of Self-Adaptive Systems: a Goal-Oriented Approach. In: International Symposium on Software Engineering for Adaptive and Self-Managing Systems. SEAMS ‘19. IEEE, 2019, pp. 89–99.
• Arut Prakash Kaleeswaran, Peter Munk, Samir Sarkic, Thomas Vogel, and Arne Nordmann. A Domain Specific Language to support HAZOP Studies of SysML Models. In: 6th International Symposium on Model-Based Safety and Assessment. IMBSA ‘19. Springer, 2019, pp. 47–62.
• Thomas Vogel. mRUBiS: An Exemplar for Model-Based Architectural Self-Healing and Self-Optimization. In: International Symposium on Software Engineering for Adaptive and Self-Managing Systems. SEAMS ’18. ACM, 2018, pp. 101–107.
• Arthur Rodrigues, Ricardo Caldas, Genaina Rodrigues, Thomas Vogel, and Patrizio Pelliccione. A Learning Approach to Enhance Assurances for Real-Time Self-Adaptive Systems. In: International Symposium on Software Engineering for Adaptive and Self-Managing Systems. SEAMS ‘18. ACM, 2018, pp. 206–216.
• Sona Ghahremani, Holger Giese, and Thomas Vogel. Efficient Utility-Driven Self-Healing Employing Adaptation Rules for Large Dynamic Architectures. In: International Conference on Autonomic Computing. ICAC ‘17. IEEE, 2017, pp. 59–68. (Karsten Schwan Best Paper Award).
• Sona Ghahremani, Holger Giese, and Thomas Vogel. Towards Linking Adaptation Rules to the Utility Function for Dynamic Architectures. In: International Conference on Self-Adaptive and Self-Organizing Systems. SASO ‘16. IEEE, 2016, pp. 142–143.
• Antonio Filieri, Martina Maggio, Konstantinos Angelopoulos, Nicolas D’Ippolito, Ilias Gerostathopoulos, Andreas Berndt Hempel, Henry Hoffmann, Pooyan Jamshidi, Evangelia Kalyvianaki, Cristian Klein, Filip Krikava, Sasa Misailovic, Alessandro Vittorio Papadopoulos, Suprio Ray, Amir M. Sharifloo, Stepan Shevtsov, Mateusz Ujma, and Thomas Vogel. Software Engineering meets Control Theory. In: International Symposium on Software Engineering for Adaptive and Self-Managing Systems. SEAMS ’15. IEEE, 2015, pp. 71–82.
• Holger Giese, Thomas Vogel, and Sebastian Wätzoldt. Towards Smart Systems of Systems. In: International Conference on Fundamentals of Software Engineering (FSEN ’15). Vol. 9392. Lecture Notes in Computer Science (LNCS). Springer, 2015, pp. 1–29. (invited paper).
• Thomas Vogel and Holger Giese. A Language for Feedback Loops in Self-Adaptive Systems: Executable Runtime Megamodels. In: International Symposium on Software Engineering for Adaptive and Self-Managing Systems. SEAMS ’12. IEEE, 2012, pp. 129–138. (selected as one of two best papers).
• Thomas Vogel, Stefan Neumann, Stephan Hildebrandt, Holger Giese, and Basil Becker. Model-Driven Architectural Monitoring and Adaptation for Autonomic Systems. In: International Conference on Autonomic Computing and Communications. ICAC ’09. ACM, 2009, pp. 67–68.
• Thomas Vogel, Jens Bruhn, and Guido Wirtz. Autonomous Reconfiguration Procedures for EJB-based Enterprise Applications. In: International Conference on Software Engineering and Knowledge Engineering. SEKE’08. Knowledge Systems Institute Graduate School, 2008, pp. 48–53.
• Jens Bruhn, Christian Niklaus, Thomas Vogel, and Guido Wirtz. Comprehensive support for management of Enterprise Applications. In: International Conference on Computer Systems and Applications. AICCSA ’08. IEEE, 2008, pp. 755–762.

Book Chapters

• Bradley Schmerl, Jesper Andersson, Thomas Vogel, Myra B. Cohen, Cecilia M.F. Rubira, Yuriy Brun, Alessandra Gorla, Franco Zambonelli, and Luciano Baresi. Challenges in Composing and Decomposing Assurances for Self-Adaptive Systems. In: Software Engineering for Self-Adaptive Systems III. Assurances. Ed. by Rogério de Lemos, David Garlan, Carlo Ghezzi, and Holger Giese. Vol. 9640. Lecture Notes in Computer Science (LNCS). Springer, 2017, pp. 64–89.
• Rogério de Lemos, David Garlan, Carlo Ghezzi, Holger Giese, Jesper Andersson, Marin Litoiu, Bradley Schmerl, Danny Weyns, Luciano Baresi, Nelly Bencomo, Yuriy Brun, Javier Camara, Radu Calinescu, Myra B. Cohen, Alessandra Gorla, Vincenzo Grassi, Lars Grunske, Paola Inverardi, Jean-Marc Jezequel, Sam Malek, Raffaela Mirandola, Marco Mori, Hausi A. Müller, Romain Rouvoy, Cecilia M. F. Rubira, Eric Rutten, Mary Shaw, Giordano Tamburrelli, Gabriel Tamura, Norha M. Villegas, Thomas Vogel, and Franco Zambonelli. Software Engineering for Self-Adaptive Systems: Research Challenges in the Provision of Assurances. In: Software Engineering for Self-Adaptive Systems III. Assurances. Ed. by Rogério de Lemos, David Garlan, Carlo Ghezzi, and Holger Giese. Vol. 9640. Lecture Notes in Computer Science (LNCS). Springer, 2017. pp. 3–30.
• Holger Giese, Thomas Vogel, Ada Diaconescu, Sebastian Götz, and Samuel Kounev. Architectural Concepts for Self-Aware Computing Systems. In: Self-Aware Computing Systems. Ed. by Samuel Kounev, Jeffrey O. Kephart, Aleksandar Milenkoski, and Xiaoyun Zhu. Springer, 2017. Chap. 5, pp. 109–147.
• Holger Giese, Thomas Vogel, Ada Diaconescu, Sebastian Götz, and Kirstie Bellman. Generic Architectures for Individual Self-Aware Computing Systems. In: Self-Aware Computing Systems. Ed. by Samuel Kounev, Jeffrey O. Kephart, Aleksandar Milenkoski, and Xiaoyun Zhu. Springer, 2017. Chap. 6, pp. 149–189.
• Holger Giese, Thomas Vogel, Ada Diaconescu, Sebastian Götz, Nelly Bencomo, Kurt Geihs, Samuel Kounev, and Kirstie Bellman. State of the Art in Architectures for Self-Aware Computing Systems. In: Self-Aware Computing Systems. Ed. by Samuel Kounev, Jeffrey O. Kephart, Aleksandar Milenkoski, and Xiaoyun Zhu. Springer, 2017. Chap. 8, pp. 237–275.
• Amel Bennaceur, Robert B. France, Giordano Tamburrelli, Thomas Vogel, Pieter J. Mosterman, Walter Cazzola, Fábio M. Costa, Alfonso Pierantonio, Matthias Tichy, Mehmet Aksit, Pär Emmanuelson, Huang Gang, Nikolaos Georgantas, and David Redlich. Mechanisms for Leveraging Models at Runtime in Self-adaptive Software. In: Models@run.time. Ed. by Nelly Bencomo, Robert B. France, Betty H. Cheng, and Uwe Assmann. Vol. 8378. Lecture Notes in Computer Science (LNCS). Springer, 2014, pp. 19–46.
• Jesper Andersson, Luciano Baresi, Nelly Bencomo, Rogério de Lemos, Alessandra Gorla, Paola Inverardi, and Thomas Vogel. Software Engineering Processes for Self-Adaptive Systems. In: Software Engineering for Self-Adaptive Systems II. Ed. by Rogério de Lemos, Holger Giese, Hausi Müller, and Mary Shaw. Vol. 7475. Lecture Notes in Computer Science (LNCS). Springer, 2013, pp. 51–75.
• Rogério de Lemos, Holger Giese, Hausi Müller, Mary Shaw, Jesper Andersson, Marin Litoiu, Bradley Schmerl, Gabriel Tamura, Norha M. Villegas, Thomas Vogel, Danny Weyns, Luciano Baresi, Basil Becker, Nelly Bencomo, Yuriy Brun, Bojan Cukic, Ron Desmarais, Schahram Dustdar, Gregor Engels, Kurt Geihs, Karl Goeschka, Alessandra Gorla, Vincenzo Grassi, Paola Inverardi, Gabor Karsai, Jeff Kramer, Antónia Lopes, Jeff Magee, Sam Malek, Serge Mankovskii, Raffaela Mirandola, John Mylopoulos, Oscar Nierstrasz, Mauro Pezzè, Christian Prehofer, Wilhelm Schäfer, Rick Schlichting, Dennis B. Smith, Joao P. Sousa, Ladan Tahvildari, Kenny Wong, and Jochen Wuttke. Software Engineering for Self-Adaptive Systems: A second Research Roadmap. In: Software Engineering for Self-Adaptive Systems II. Ed. by Rogério de Lemos, Holger Giese, Hausi Müller, and Mary Shaw. Vol. 7475. Lecture Notes in Computer Science (LNCS). Springer, 2013, pp. 1–32.
• Holger Giese, Leen Lambers, Basil Becker, Stephan Hildebrandt, Stefan Neumann, Thomas Vogel, and Sebastian Wätzoldt. Graph Transformations for MDE, Adaptation, and Models at Runtime. In: Formal Methods for Model-Driven Engineering. Ed. by Marco Bernardo, Vittorio Cortellessa, and Alfonso Pierantonio. Vol. 7320. Lecture Notes in Computer Science (LNCS). Springer, 2012, pp. 137–191.

Workshops

• Bento R. Siqueira, Fabiano C. Ferrari, Thomas Vogel, and Rogério de Lemos. Micro-controllers: Promoting Structurally Flexible Controllers in Self-Aware Computing Systems. In: 1st International Conference on Autonomic Computing and Self-Organizing Systems Companion. ACSOS-C ’20. IEEE, 2020, pp. 188–193.
• Thomas Vogel, Stephan Druskat, Markus Scheidgen, Claudia Draxl, and Lars Grunske. Challenges for Verifying and Validating Scientific Software in Computational Materials Science. In: International Workshop on Software Engineering for Science (co-located with ICSE ‘19). SE4Science ‘19. IEEE, 2019, pp. 25–32.
• Timo Kehrer, Andreas Vogelsang, Thomas Vogel, and Heiko Dörr. Zum fehlenden Architekturverständnis über Implementierungsmodelle multifunktionaler eingebetteter Systeme in der industriellen Praxis. In: Tagungsband des Dagstuhl-Workshops Modellbasierte Entwicklung eingebetteter Systeme XIV. MBEES ’18. pp. 1-6.
• Joachim Hänsel, Thomas Vogel, and Holger Giese. A Testing Scheme for Self-Adaptive Software Systems with Architectural Runtime Models. In: International Conference on Self-Adaptive and Self-Organizing Systems Workshops. SASOW ’15. IEEE, 2015, pp. 134–139.
• Thomas Vogel and Holger Giese. On Unifying Development Models and Runtime Models. In: International Workshop on Models@run.time. Vol. 1270. CEUR Workshop Proceedings. CEUR-WS.org, 2014, pp. 5–10.
• Thomas Vogel and Holger Giese. Requirements and Assessment of Languages and Frameworks for Adaptation Models. In: Models in Software Engineering, Workshops and Symposia at MoDELS 2011, Reports and Revised Selected Papers. Ed. by Jörg Kienzle. Vol. 7167. Lecture Notes in Computer Science (LNCS). Springer, 2012, pp. 167–182.
• Thomas Vogel and Holger Giese. Language and Framework Requirements for Adaptation Models. In: International Workshop on Models@run.time. Vol. 794. CEUR Workshop Proceedings. CEUR-WS.org, 2011, pp. 1–12. (best paper).
• Thomas Vogel, Andreas Seibel, and Holger Giese. The Role of Models and Megamodels at Runtime. In: Models in Software Engineering, Workshops and Symposia at MODELS 2010, Reports and Revised Selected Papers. Ed. by Juergen Dingel and Arnor Solberg. Vol. 6627. Lecture Notes in Computer Science (LNCS). Springer, 2011, pp. 224–238.
• Thomas Vogel and Holger Giese. Adaptation and Abstract Runtime Models. In: International Workshop on Software Engineering for Adaptive and Self-Managing Systems. SEAMS ’10. ACM, 2010, pp. 39–48.
• Thomas Vogel, Stefan Neumann, Stephan Hildebrandt, Holger Giese, and Basil Becker. Incremental Model Synchronization for Efficient Run-Time Monitoring. In: Models in Software Engineering, Workshops and Symposia at MODELS 2009, Reports and Revised Selected Papers. Ed. by Sudipto Ghosh. Vol. 6002. Lecture Notes in Computer Science (LNCS). Springer, 2010, pp. 124–139.
• Thomas Vogel, Andreas Seibel, and Holger Giese. Toward Megamodels at Runtime. In: International Workshop on Models@run.time. Vol. 641. CEUR Workshop Proceedings. CEUR-WS.org, 2010, pp. 13–24. (best paper).
• Thomas Vogel, Stefan Neumann, Stephan Hildebrandt, Holger Giese, and Basil Becker. Incremental Model Synchronization for Efficient Run-time Monitoring. In: International Workshop on Models@run.time. Vol. 509. CEUR Workshop Proceedings. CEUR-WS.org, 2009, pp. 1–10. (best paper).
• Holger Giese, Andreas Seibel, and Thomas Vogel. A Model-Driven Configuration Management System for Advanced IT Service Management. In: International Workshop on Models@run.time. Vol. 509. CEUR Workshop Proceedings. CEUR-WS.org, 2009, pp. 61–70.

Artifacts

• Thomas Vogel. mRUBiS: An Exemplar for Model-Based Architectural Self-Healing and Self-Optimization (Artifact). In: Dagstuhl Artifacts Series (DARTS) 4.1 (2018), Schloss Dagstuhl–Leibniz-Zentrum fuer Informatik, pp. 2:1–2:4.

Technical Reports

• Sonja Cornelsen, Thomas Vogel, and Dennis Guck. Abschlussbericht des Verbundvorhabens Safe.Spec – Qualitätssicherung von Verhaltensanforderungen. Tech. rep. 01IS16027A/01IS16027B. TWT GmbH Science & Innovation und Humboldt-Universität zu Berlin, 2019.
• Javier Camara, David Garlan, Shihong Huang, Masako Kishida, Alberto Leva, Alessandro Vittorio Papadopoulos, Yasuyuki Tahara, Kenji Tei, Thomas Vogel, and Danny Weyns. Bridging the Gap between Control and Self- Adaptive System Properties: Identification, Characterization, and Mapping. Report of the 2nd National Institute of Informatics (NII) Shonan Meeting on Controlled Adaptation of Self-Adaptive Systems (CASaS). Tokyo, Japan, 2017.
• Thomas Vogel and Holger Giese. Model-Driven Engineering of Adaptation Engines for Self-Adaptive Software: Executable Runtime Megamodels. Tech. rep. 66. Hasso Plattner Institute at the University of Potsdam, Germany, 2013.
• Rogério de Lemos, Holger Giese, Hausi Müller, Mary Shaw, Jesper Andersson, Luciano Baresi, Basil Becker, Nelly Bencomo, Yuriy Brun, Bojan Cukic, Ron Desmarais, Schahram Dustdar, Gregor Engels, Kurt Geihs, Karl Goeschka, Alessandra Gorla, Vincenzo Grassi, Poala Inverardi, Gabor Karsai, Jeff Kramer, Marin Litoiu, Antónia Lopes, Jeff Magee, Sam Malek, Serge Mankovskii, Raffaela Mirandola, John Mylopoulos, Oscar Nierstrasz, Mauro Pezzè, Christian Prehofer, Wilhelm Schäfer, Wilhelm Schlichting, Bradley Schmerl, Dennis B. Smith, Joao P. Sousa, Gabriel Tamura, Ladan Tahvildari, Norha M. Villegas, Thomas Vogel, Danny Weyns, Kenny Wong, and Jochen Wuttke. Software Engineering for Self-Adpaptive Systems: A second Research Roadmap. In: Software Engineering for Self-Adaptive Systems. Ed. by Rogério de Lemos, Holger Giese, Hausi Müller, and Mary Shaw. Dagstuhl Seminar Proceedings 10431. Schloss Dagstuhl - Leibniz-Zentrum fuer Informatik, Germany, 2011. (draft version of May 20, 2011).