Tom Leinster

http://www.maths.ed.ac.uk/~tl

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Where is number theory used in the rest of mathematics?

nt.number-theory soft-question big-list asked Mar 9, 2012 at 14:50

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63 votes

Unnecessary uses of the axiom of choice

set-theory lo.logic big-list axiom-of-choice asked Feb 17, 2022 at 21:12

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60 votes

Why are abelian groups amenable?

gr.group-theory measure-theory asked Jan 18, 2010 at 3:02

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55 votes

Bizarre operation on polynomials

ac.commutative-algebra polynomials asked Jan 20, 2010 at 1:39

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54 votes

Is there an odd-order group whose order is the sum of the orders of the proper normal subgroups?

finite-groups gr.group-theory nt.number-theory asked Feb 9, 2011 at 5:50

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47 votes

What examples of distributions should I keep in mind?

schwartz-distributions intuition ca.analysis-and-odes asked Nov 9, 2009 at 3:18

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43 votes

What are some examples of proving that a thing exists by proving that the set of such things has positive measure?

big-list examples asked Jul 14, 2020 at 19:01

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39 votes

Is there a truly general voting impossibility theorem that applies to real elections?

social-choice voting-theory asked Jul 15, 2014 at 11:33

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32 votes

What are the algebras for the double dualization monad?

ct.category-theory linear-algebra asked Aug 15, 2012 at 17:03

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32 votes

How is the Julia set of $fg$ related to the Julia set of $gf$?

ds.dynamical-systems complex-dynamics complex-analysis asked Jan 2, 2012 at 12:58

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Top Answers

128

What properties make $[0,1]$ a good candidate for defining fundamental groups?

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When is $A$ isomorphic to $A^3$?

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Best online mathematics videos?

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When are two proofs of the same theorem really different proofs

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Theorems for nothing (and the proofs for free)

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Cures for mathematician's block (as in writer's block)

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Taking lecture notes in lectures

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How do I check if a functor has a (left/right) adjoint?

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What is a metric space?

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What are the benefits of viewing a sheaf from the "espace étalé" perspective?

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Is the ultraproduct concept fundamentally category-theoretic?

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Expressing the Lebesgue integral using categories + the difficulty of describing estimates in category theory

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Google question: In a country in which people only want boys

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What is the name of the following categorical property?

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Can epi/mono for natural transformations be checked pointwise?

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What's a groupoid? What's a good example of a groupoid?

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Good lattice theory books?

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Combinatorial results without known combinatorial proofs

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"Philosophical" meaning of the Yoneda Lemma

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Coend computation

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Is a functor which has a left adjoint which is also its right adjoint an equivalence ?

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Can the opposite of an elementary topos be an elementary topos?

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What's a magical theorem in logic?

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Geometric interpretations of the exponential of entropy

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Continuous function from $[0,1]$ to $[0,1]$

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Citation of a paper with a proof you would like to improve

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Are there categories whose internal hom is somewhat 'exotic'?

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Terminology in category theory

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What is the general opinion on the Generalized Continuum Hypothesis?

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What is known about the category of monads on Set?

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