1. M. P. F. du Sautoy, J. J. McDermott, and G. C. Smith, Zeta functions of crystallographic groups and analytic continuation, Proc. London Math. Soc. (3) 79 (1999), no. 3, 511–534.[MR]
  2. Marcus du Sautoy and Luke Woodward, Nilpotent groups: explicit examples, Zeta Functions of Groups and Rings, Lecture Notes in Computer Science, vol. 1925/2008, Springer Berlin / Heidelberg, 2008, pp. 21–68.