- Author: Astrid Sigel (editor), Helmut Sigel (editor), Roland K.O. Sigel (editor)
- Language: English
- Year: 2015
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- Language: English
- Year: 2021
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- Language: English
- Year: 2015
- Author: Astrid Sigel (editor), Eva Freisinger (editor), Roland K.O. Sigel (editor)
- Language: English
- Year: 2021
- Author: Astrid Sigel (editor), Helmut Sigel (editor), Roland K.O. Sigel (editor)
- Language: English
- Year: 2015
- Author: Astrid Sigel (editor), Helmut Sigel (editor), Roland K.O. Sigel (editor)
- Language: English
- Year: 2015
- Author: Astrid Sigel (editor), Helmut Sigel (editor), Roland K.O. Sigel (editor)
- Language: English
- Year: 2015