Oct 5, 2011 · Is there a listing of open problems in math? Let me make myself clearer. I'm a grad student and I want to train my abilities with not yet solved problems. So is there a list, or a book or …

Apr 15, 2021 · This characterization works well for intervals because they are convex (notice the demo uses midpoint), but it's not much different for general open sets in $\mathbb R^n$. See a closed set …

Jan 16, 2025 · This question shows research effort; it is useful and clear

Dec 24, 2020 · A disc in $\Bbb R^2$ is 2D, whereas a spherical hemisphere in $\Bbb R^3$ is not 3D. If you pick an open ball in $\Bbb R^3$, then all of the tangent spaces may be identified with $\Bbb …

May 22, 2025 · Problem somewhat related to this post, and I refer to the same exercise in John Lee's Introduction to Smooth Manifolds. My issue is trying to understand the relationship between a …

Jan 22, 2015 · 2 'Not closed' does not mean open, for example the set $ [0,1)$ is neither open nor closed. And, as you suggest, sets can be both open and closed (as both $\varnothing$ and $\mathbb …

I'm interested in finding a math-related open source project that I can contribute to. I've studied maths and stats at undergraduate level, but I'm a professional software developer and I'll have some spare …

Dec 4, 2025 · My question is this. Why is it the sum of two semi-continuous functions, in general, may not be semi-continuous? I am trying to construct such two examples of semi-continuous functions …

Dec 11, 2025 · In my intro alg. geo class, o so many years ago, the prof recounted how the influential algebraic geometer Solomon Lefschetz, having since changed his field of study (many times), would …

Aug 11, 2016 · It is complex? Do you have a reference? I figured I could split the Gamma integral into positive and negative parts. Numerical Recipes then has some routines for evaluating the parts, but I …