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- Language: English
- Year: 2001
- Author: Ralph H. Estey
- Language: English
- Year: 1994
- Author: Ralph Heintzman
- Language: English
- Year: 2011
- Author: R. M. H. McMinn, Ralph T. Hutchings
- Language: Czech
- Author: Barczok Ralph Barczok
- Language: German
- Year: 2021
- Author: Ralph Barczok
- Language: German
- Year: 2021
- Author: Ralph Woodrow
- Language: Spanish
- Year: 2008
- Author: Ralph W. G. Wyckoff
- Language: English
- Year: 1968
- Author: Ralph Tegtmeier
- Language: German
- Year: 1989