Tài liệu tham khảo WikiPedia: Âu_Việt http://books.google.com/books?id=Jskyi00bspcC&pg=P... http://books.google.com/books?id=V4YyosYY9WIC&pg=P... http://truongthaidu.wordpress.com/2008/03/17/th%E1... http://vietnamnet.vn/vn/doi-song/101365/cao-bang-v...