18 Answers votes newest views recent 16Non-commutator in simple group? 13How many elements does it take to normally generate a group? 10Connections between ultrafilters in topology and logic 7Do you know how to construct a compact hyperbolic 3-manifold with three or four totally geodesic boundary components? 6Example of a manifold which is not a homogeneous space of any Lie group 6A name for a weak topology 5When does a homomorphism factor through a free group? 5Isometries between metric spaces 5The number of cusps of higher-dimensional hyperbolic manifolds 5Is the cut locus of a generic point in a hyperbolic manifold a generic polyhedron? 5Is there a combinatorial analogue of Ricci flow? 4When does Cantor-Bernstein hold? 4center of fundamental group of finite volume-hyperbolic orbifold 3Can anyone give me a good example of two interestingly different ordinary cohomology theories? 3fundamental groups of surfaces 3Is there a quaternionic algebraic geometry ? 1Is there a “knot theory” for graphs? 1Can the fundamental group of an intersection of a homeomorphic image of a ball with a complement of a ball in $R^3$ be perfect?