@Article{BeSa95,
  author = 	 "Fran{\c{c}}ois Bergeron and Ulrike Sattler",
  title = 	 "Constructible differentially finite algebraic series in
		  several variables",
  journal = 	 TCS,
  year = 	 "1995",
  volume =	 144,
  number =	 "1-2",
  month =	 "June",
  pages =	 "59-66"
}