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Questions designed to generate a "big list" of certain results, examples, conjectures, etc. via many individual answers, each contributing one or a few instances. Such a question should typically be in Community Wiki mode (CW); after asking, please, flag for moderators attention requesting the question to be made CW.

-3 votes

Suggestions for good notation

I like the notation $f:A\cong\subseteq B$ for "$f$ is an embedding of $A$ into $B$." The idea is that the relation of embeddability is obtained by composing the relations "isomorphic to" and "substru …
30 votes

Theorems first published in textbooks?

Long ago, I proved that every derivation from $C^{k+1}$ functions to $C^k$ functions is given by a $C^k$ vector field. (The same fact with $\infty$ in place of $k$ and $k+1$ is, of course, classical. …
21 votes

Nonequivalent definitions in Mathematics

An extension of a group $A$ by a group $B$ can be either a group $G$ with a normal subgroup isomorphic to $B$ with $G/B$ isomorphic to $A$ or a group $G$ with a normal subgroup isomorphic to $A$ with …
21 votes

Never appeared forthcoming papers

Dana Scott and Robert Solovay, "Boolean-valued models of set theory"
9 votes

German mathematical terms like "Nullstellensatz"

"Urelement" is used in set theory as a fancy name for an atom, i.e., something that can be a member of a set but is not itself a set.
252 votes

What are some examples of colorful language in serious mathematics papers?

Does merely transposing two words count? "It is also hard not to show that ..." [Arnold W. Miller, "Some Properties of measure and category," Trans. A.M.S. 266, 1981, p. 106]
7 votes

Which math paper maximizes the ratio (importance)/(length)?

Lawvere's paper "Quantifiers and sheaves" (1970 International Congress of Mathematicians at Nice, vol. 1, pp. 329--334) was the first publication of his work with Tierney on elementary topoi. It cont …
6 votes

Dimension leaps

The free modular lattice on $n$ generators is finite for $n=1,2,3$, but for $n=4$ not only is it infinite but its word problem is recursively unsolvable.
13 votes

Pseudonyms of famous mathematicians

I'm not sure whether to count as pseudonyms the altered names that people took (often to avoid antisemitic prejudice) as replacements for their real names. For example, Alfred Tarski's last name was …
10 votes

Important results with one or more than one proof

The first example that occurs to me is Hindman's theorem: If the set of positive integers is partitioned into finitely many pieces, then there is an infinite set $H$ such that all sums of finitely man …
10 votes

Examples of $G_\delta$ sets

In the space of all subsets of $\mathbb{N}$ (identified via characteristic functions with $2^{\mathbb{N}}$ and topologized as the product of copies of the discrete 2-point space), the set of infinite …
Andreas Blass's user avatar
22 votes

Examples of theorems with proofs that have dramatically improved over time

I described an example, Hindman's theorem, at https://mathoverflow.net/questions/94546 . The short version is that Hindman's original proof was unpleasantly complicated, whereas a later proof by Galv …
3 votes

How should the Math Subject Classification (MSC) be revised or improved?

My experience has been that the editors of Math Reviews pay attention to suggestions about revisions of the classification system. I'm not saying that they implement all the suggestions (especially b …
9 votes

Mathematical ideas named after places

anarboricity of graphs (named in honor of the city of Ann Arbor by Frank Harary, but also having something to do with non-trees (http://mathworld.wolfram.com/Anarboricity.html)
1 vote

Mathematical ideas named after places

The Conway-Paterson-Moscow theorem

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