Hans Pfitzner--"Das Herz" und der Übergang zum Spätwerk: Bericht über das Symposion Rudolstadt 1993 (Veröffentlichungen der Hans-Pfitzner-Gesellschaft)
Books can be attributed to "Unknown" when the author or editor (as applicable) is not known and cannot be discovered. If at all possible, list at least one actual author or editor for a book instead of using "Unknown".
Books whose authorship is purposefully withheld should be attributed instead to Anonymous.