A function $f \in L^1(\mathbb R^n)$ is said to be of bounded variation if there exists a constant $C \geq 0$ such that $$ \int_{\mathbb R^n} f(x) \operatorname{div} \phi(x) \; dx \leq C \sup_{ x \in \mathbb R^n } \lvert\phi(x)\rvert $$ for all compactly supported differentiable vector fields $\p...

Given an initial integer $x_0>0$, one can consider the first prime of the recursive sequence $x_i=1+2x_{i-1}$. Naïvely such a prime should exist for $x_0$ arbitrary since the sequence $\log(x_i)$ is asymptotically an arithmetic progression. Sometimes it takes however some time: for $x_0=147$ my M...

The ask page tag input box currently looks like this: The old ask page on MO 1.0 had a much more detailed description of what top-level tags on MO are: Since appropriate tagging on MO can be confusing to new users, it would be great to reintroduce top-level tag suggestions on the ask page.

There is a feature of showing suggested tags after the body of a question is included. These suggestions are based on the body of the question. More details can be found in these posts: Automatically determine tags while writing a question How are “Suggested Tags” chosen? I will quote part of o...

In the last few months, Stack exchange has introduced tag warnings, that is, a text that is displayed when a user creates a new question that contains a specific warning, such as this example. Apparently, the feature has been introduced without a formal announcement by the SE team (or at least...

Let me first say, that I consider links to papers referenced in MO posts a useful things. And so do other users, judging by an older discussion on this topic: Is it worth editing old posts to add links for references? Occasionally you can find links which contain part related to proxy of a speci...

Links to Mathscinet and other similar sources cannot be "fixed" to work for all. Mathscinet indeed requires subscription. The ways to use it varies from one university to another and sometimes depend on where you use it from. Some use proxies, others use passwords etc. For this reasons, I try no...