- Author: Rudolf Ritsema, Shantena Augusto Sabbadini
- Language: English
- Year: 2018
- Author: Shantena Augusto Sabbadini Rudolf Ritsema
- Language: English
- Year: 2005
- Author: Rudolf Ritsema, Shantena Augusto Sabbadini
- Language: English
- Year: 2018
- Author: Adolf Portmann Rudolf Ritsema
- Language: german, english, french
- Year: 1975