#### Volume 2, issue 1 (2002)

 1 I Agol, D D Long, A W Reid, The Bianchi groups are separable on geometrically finite subgroups, Ann. of Math. $(2)$ 153 (2001) 599 MR1836283 2 A Borel, Compact Clifford–Klein forms of symmetric spaces, Topology 2 (1963) 111 MR0146301 3 A Borel, Harish-Chandra, Arithmetic subgroups of algebraic groups, Ann. of Math. $(2)$ 75 (1962) 485 MR0147566 4 L S Charlap, Bieberbach groups and flat manifolds, Universitext, Springer (1986) MR862114 5 F T Farrell, S Zdravkovska, Do almost flat manifolds bound?, Michigan Math. J. 30 (1983) 199 MR718265 6 M Gromov, Almost flat manifolds, J. Differential Geom. 13 (1978) 231 MR540942 7 G C Hamrick, D C Royster, Flat Riemannian manifolds are boundaries, Invent. Math. 66 (1982) 405 MR662600 8 T Y Lam, The algebraic theory of quadratic forms, W. A. Benjamin, Reading, MA (1973) MR0396410 9 D D Long, Immersions and embeddings of totally geodesic surfaces, Bull. London Math. Soc. 19 (1987) 481 MR898729 10 D D Long, A W Reid, On the geometric boundaries of hyperbolic 4–manifolds, Geom. Topol. 4 (2000) 171 MR1769269 11 B E Nimershiem, All flat three-manifolds appear as cusps of hyperbolic four-manifolds, Topology Appl. 90 (1998) 109 MR1648306 12 J G Ratcliffe, Foundations of hyperbolic manifolds, Graduate Texts in Mathematics 149, Springer (1994) MR1299730 13 J G Ratcliffe, S T Tschantz, The volume spectrum of hyperbolic 4–manifolds, Experiment. Math. 9 (2000) 101 MR1758804 14 W P Thurston, Three-dimensional geometry and topology Vol. 1, Princeton Mathematical Series 35, Princeton University Press (1997) MR1435975 15 È B Vinberg, The groups of units of certain quadratic forms, Mat. Sb. $($N.S.$)$ 87(129) (1972) 18 MR0295193 16 È B Vinberg, O V Shvartsman, Discrete groups of motions of spaces of constant curvature, from: "Geometry, II", Encyclopaedia Math. Sci. 29, Springer (1993) 139 MR1254933