I'm (planning on) writing a paper about the feasibility of the Schlieffen Plan and it's potential for victory, but the assignment requires a certain number of primary sources. This doesn't seem like the kind of topic where a general would keep a diary of his exact thoughts. But are there primary sources that would be useful for a student writing a short essay? Or is working through primary sources in this area more the work of a professional historian? Essentially I need help finding readings on the subject, because there seem to be an abundance of secondary sources, but not primary.