- Author: Humberto Maturana Rumesin Bernhard Poerksen
- Language: English
- Year: 2004
- Author: Luhmann Niklas
- Language: German
- Year: 2008
- Author: Bernhard Pörksen
- Language: German
- Year: 2008
- Author: Manfred Prior
- Language: German
- Year: 2004
- Author: Heinz von Foerster
- Language: German
- Year: 2001