20 Answers votes newest views recent 27What should be offered in undergraduate mathematics that’s currently not (or isn’t usually)? 3Lie Groups and Manifolds 8What’s an example of a space that needs the Hahn-Banach Theorem? 4can you fool SnapPea? 17Is a subgroup of a free abelian group free abelian? 5When is a Riemannian metric equivalent to the flat metric on $\mathbb R^n$? 3Symmetrical Presentation of 4-Dimensional Rotation Matrix 2What’s a non-abelian totally ordered group? 2Minimal surface in a ball 6Independence of the continuum hypothesis on ZFC 3Why is the standard definition of cocycle the one that _always_ comes up?? 8Algorithm generalizing continued fractions for non-quadratic algebraic numbers 10Circle bundles over $RP^2$ 6Dolbeault cohomology 6What are CR manifolds like? 2What is an example of a function on M_g? 9Rational Group Cohomology 3Stable w-length 6Is there a simplicial volume definition of Chern Simons invariants? 9What is the right way to think about / represent general tilings?