How to clean duplicates existing in one folder from another recursively?

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http://askubuntu.com – Summary: Folder A has only many Excelent files Folder B has many folders of mixed Excelent/Good/Bad files How can i delete files in Folder B folders only in case they will be in Folder A. Or simply putting same thing: How to make checking of Folder A files if they exist in Folder B folders then delete from Folder B folders? Idea of solution Maybe a command witch: Checks part of alphabet like all starting with A Executing deletion on files found in Folder B subfolders Repeat 1. + one alphabet up. Cause duplication programs were bad: Long time until 1st deletion- its only when finished sc (HowTos)