The participants of the August 1999 conference on the 3x+1 problem and related topics, kindly hosted by the Eichstätt university in Germany.
From left to right:

• K. M. Monks, USA, participant
• Ken G. Monks, University of Scranton (USA), speaker
• Paul Andaloro, Kent State University (USA), speaker
• Günther Wirsching, Eichstätt (Germany), organiser and speaker
• Manfred Kudlek, Universität Hamburg (Germany), speaker
• Ranan Banerji, St Joseph's University (USA), speaker
• Jeffrey Lagarias, AT&T Labs (USA), invited speaker
• Dierk Schleicher,Universität München (Germany), speaker
• Marc Chamberland, Grinnell College, Iowa (USA), organiser and speaker
• Jean-Louis Rouet, Université de Orléans (France), speaker
• Eric Roosendaal, Amsterdam (Netherlands), speaker
• U. Fitze, Switzerland, participant
• Marc Feix, École des Mines de Nantes (France), speaker
• Edward Belaga, Université de Strasbourg (France), speaker