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Dan Petersen's user avatar
Dan Petersen
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86
Examples where it's useful to know that a mathematical object belongs to some family of objects
Sep 1, 2011
answer
72
Structures that turn out to exhibit a symmetry even though their definition doesn't
Dec 14, 2013
answer
68
Can the fundamental group of any manifold be realized as the fund grp of a finite space?
Nov 10, 2010
question
50
What (if anything) unifies stable homotopy theory and Grothendieck's six functors formalism?
Jun 8, 2014
answer
49
Ring-theoretic characterization of open affines?
Apr 8, 2010
answer
48
Most memorable titles
Oct 31, 2010
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42
How did the refereeing system of Gösta Mittag-Leffler's Acta Mathematica function from 1882 to (about) 1918?
Jul 12, 2017
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41
Elementary proof that $\mathbb{R}^3 \setminus \{p_1,\dots,p_n\}$ is not homeomorphic to $\mathbb{R}^3$
Jan 6, 2021
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39
What does the term "yoga" mean in mathematics?
May 6, 2011
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The "derived drift" is pretty unsatisfying and dangerous to category theory (or at least, to me)
Dec 26, 2017
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When a MSE user is suspended, should the suspension apply to MO as well?
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Why do they think this question is not of research level?
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Why do mathematicians use single-letter variables?
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How to prove that a polynomial of degree $n$ has at most $n$ roots?
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Does $\zeta(3)$ have a connection with $\pi$?
26
Are there any non-constructive proofs for which an example was never constructed?
25
A challenge by R. P. Feynman: give counter-intuitive theorems that can be translated into everyday language