bibliography Allen, David: Getting Things Done: The Art of Stress-Free Productivity, New York: Penguin Books, 2001. Beatty, Jack: The World According to Peter Drucker, New York: Broadway Books, 1998. Beaujean, Alfred, Beer, Monika, et al.: Harenberg Opernführer: Der Schlüssel zu 500 Opern, ihrer Handlung und Geschichte, 3rd revised and expanded edition, Dortmund, Germany: Harenberg Verlag, 2002. Beaujean, Alfred, Brembeck, Reinhard, et al.: Harenberg Konzertführer: Der Schlüssel zu 600 Werken von 200 Komponisten, 6th edition, Dortmund, Germany: Harenberg Verlag, 2001. Beer, Stafford: The Heart of Enterprise, 4th edition, Chichester, UK: John Wiley & Sons, 2000. Bennis, Warren: On Becoming a Leader, Reading, MA: Perseus Books, 1994.