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- Language: German
- Year: 1930

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- Language: German
- Year: 1929

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- Language: German
- Year: 1925

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- Language: German
- Year: 1961

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- Language: German
- Year: 1926

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- Language: German
- Year: 1927

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- Language: German
- Year: 1933

- Author: Nicolaas Wijk
- Language: German
- Year: 1931

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- Language: German
- Year: 1933

- Author: Bogdan Dimitrov Filov
- Language: German
- Year: 1932