Journal Article Computability in Europe 2009 Get access Klaus Ambos-Spies, Klaus Ambos-Spies Institut für Informatik, Universität Heidelberg, Im Neuenheimer Feld 294, 69120 Heidelberg, Germany. E-mail: ambos@math.uni-heidelberg.de Search for other works by this author on: Oxford Academic Google Scholar Arnold Beckmann, Arnold Beckmann Department of Computer Science, College of Science, Swansea University, Singleton Park, Swansea SA2 8PP, UK. E-mail: a.beckmann@swansea.ac.uk Search for other works by this author on: Oxford Academic Google Scholar Erzsébet Csuhaj-Varjú, Erzsébet Csuhaj-Varjú Computer and Automation Research Institute, Hungarian Academy of Sciences, Kende u 13-17, H-1111 Budapest, Hungary. E-mail: csuhaj@sztaki.hu Search for other works by this author on: Oxford Academic Google Scholar Benedikt Löwe Benedikt Löwe Institute for Logic, Language and Computation, Universiteit van Amsterdam, Postbus 94242, 1090 GE Amsterdam, The Netherlands; Department Mathematik, Universität Hamburg, Bundesstrasse 55, 20146 Hamburg, Germany. E-mail: bloewe@science.uva.nl Search for other works by this author on: Oxford Academic Google Scholar Journal of Logic and Computation, Volume 23, Issue 4, August 2013, Pages 727–728, https://doi.org/10.1093/logcom/exr051 Published: 15 July 2013