1. M. R. Bridson and C. F. Miller III, “Structure and finiteness properties of subdirect products of groups,” Proc. London Math. Soc. (3) 98(3), 631–651 (2009).
2. C. F. Miller III, On Group-Theoretic Decision Problems and Their Classification, in Ann. Math. Stud. (Princeton Univ. Press, Princeton, NJ, 1971), Vol. 68.
3. G. Baumslag, M. R. Bridson, C. F. Miller III and H. Short, “Fibre products, non-positive curvature, and decision problems,” Comment. Math. Helv. 75(3), 457–477 (2000).
4. K. Igusa, The Generalized Grassmann Invariant, Preprint (Brandeis Univ., Waltham, MA, 1979).
5. Lecture Notes in Math;C P Rourke,1979