New posts in big-list

Examples of subgroups where it's nontrivial to show closure under multiplication?

Daily exercises to speed up my mental calculations?

Neat solutions to tedious questions

In which topologies do open sets maintain open under countable or arbitrary intersection?

A list of Rudin-style textbooks

Problems with seemingly not enough information

Problems with interesting, non-trivial analogues in finite fields

What calculation shortcuts exist to help or speed-up mental (or paper) calculations?

Examples of non-constructive results

Examples of open problems solved through short proof

Show me some pigeonhole problems [closed]

Mathematics and literature [closed]

Good (Auto)Biographies of von Neumann and other physicists/mathematicians

Why do we consider prime numbers important, and what are their applications other than number theory in pure math?

What is the theorem that has the most proofs?

Examples of fallacies in arithmetic and/or algebra [closed]

Discrepancies in mathematical definitions. [closed]

Examples of bi-implications ($\Leftrightarrow$) where the $\Rightarrow$ direction is used in the proof of the $\Leftarrow$ direction.

Is there more to complex analysis than a two-dimensional potential theory?

What are some easily-stated recently proven theorems? [closed]