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awarded  Good Question 
Mar 3 
awarded  Famous Question 
Mar 2 
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On the coherence theorem for bicategories
If you want a quick overview of the situation, you could try the slides here, especially pages 8 and 14: maths.ed.ac.uk/~tl/toronto 
Jan 22 
awarded  Popular Question 
Jan 18 
awarded  Good Answer 
Jan 17 
awarded  Enlightened 
Jan 16 
awarded  Nice Answer 
Dec 2 
awarded  Notable Question 
Dec 1 
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History of integral notation for coends
Do you know how we came to write the end variable at the bottom of the integral sign and the coend variable at the top? 
Dec 1 
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What theorem constructs an initial object for this category? (Formerly “Integrability by abstract nonsense”)
@IanMorris Thanks for pointing out the dead link. I still haven't got round to publishing it, but meanwhile I've proved some further results: maths.ed.ac.uk/~tl/cambridge_ct14 and golem.ph.utexas.edu/category/2014/07/… 
Nov 30 
awarded  Nice Answer 
Nov 27 
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Realizing a monoid as $\mathrm{End}(G)$ for some graph $G$
To add some info on Adam's remarks: for Adámek and Rosický, a graph is a set endowed with a binary relation and a homomorphism is a function preserving the binary relation. More concretely put, their graphs are directed, can have loops but cannot have multiple edges, and may be infinite. They give that definition on p.10. The section on embedding into graphs, which presumably contains the results Adam mentions, is section 2.G. 
Nov 27 
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a question about connected open sets in $R^2$
Oh, oops. I misread it. 
Nov 27 
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a question about connected open sets in $R^2$
Surely the answer is an easy "no". Just take $U$ and $V$ to be disjoint. Am I missing something? 
Nov 27 
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Realizing a monoid as $\mathrm{End}(G)$ for some graph $G$
Do you want to be specific about what you mean by "graph", or are you leaving it openended? 
Nov 20 
awarded  Nice Answer 
Nov 9 
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What measurable quantity can constrain the number of odors human can discriminate?
I'm dismayed at the votes to close and Stefan's critique. Yoav carefully explained the issues in such a way that a mathematician with no knowledge of this biological system could make a meaningful contribution. If we close this question, we might as well put a banner on the front page saying "applied math questions not welcome here". 
Oct 24 
answered  Topological characterization of injective metric spaces 
Oct 23 
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Characterize the category of rings
@Paul Yes! That was why I assumed that I wasn't really answering Chris's question. As you say, it's kind of a tautological statement. 
Oct 23 
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Characterize the category of rings
OK: the category of rings together with its forgetful functor to $\mathbf{Set}$ is terminal among all categories $C$ equipped with a functor $U: C \to \mathbf{Set}$ and a ring structure on the object $U \in [C, \mathbf{Set}]$! That's probably not the kind of thing you want, though... 