:Nice to hear your comments User:Gerda Arendt. The source being used here is Professor George Stauffer from Rutgers University in the U.S. He has written a good book review of the new Bach book by Gardiner Music in the Castle of Heaven. At 600 pages it is one of the best studies on the Cantatas in recent years. The book review itself might be found electronically on the website for The New York Review of Books in the current issue. It should at least give you more details about the source if this helps out.