- Author: Christensen Ralph, Kudlich Hans
- Language: German
- Year: 2008
- Author: Bayer Ralph-Christopher, Reichl Norbert
- Language: German
- Year: 1997
- Author: Balzer Ralph
- Language: German
- Year: 2009
- Author: Ralph Brucker
- Language: German
- Year: 1997
- Author: Ralph Meier
- Language: German
- Year: 1997
- Author: Ralph Jessen
- Language: German
- Year: 1999