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  3. Mathias Kratzer, Konkrete Charaktertafeln und kompatible Charaktere, Vorlesungen aus dem Fachbereich Mathematik der Universität GH Essen [Lecture Notes in Mathematics at the University of Essen], vol. 30, Universität Essen Fachbereich Mathematik, Essen, 2001, pp. vi+106.[MR]
  4. Mathias Kratzer, Uniform and natural existence proofs for Janko's sporadic groups J2 and J3, Arch. Math. (Basel) 79 (2002), no. 1, 5–18.[MR]
  5. Mathias Kratzer, Constructing pairs of compatible characters, in Proceedings of the First Sino-German Workshop on Representation Theory and Finite Simple Groups (Beijing, 2002), vol. 10, 2003, pp. 285–302.[MR]
  6. Mathias Kratzer, Wolfgang Lempken, Gerhard O. Michler, and Katsushi Waki, Another existence and uniqueness proof for McLaughlin's simple group, J. Group Theory 6 (2003), no. 4, 443–459.[MR]