48

Answers
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28
Why are matrices ubiquitous but hypermatrices rare?
17
Sexy vacuity …
16
Is there a “disjoint union” sigma algebra?
13
Abstract Thought vs Calculation
12
Can we have A={A} ?
12
Is it possible to construct (without choice, even?) a non-finitely-generated group with no proper non-finitely-generated subgroup?
12
Simple adjective for “of the size of a proper class”?
9
compact-open topology
8
Locally a topos
8
Indecomposable objects in a category
7
Geometric intuition for limits
7
Non-examples of model structures, that fail for subtle/surprising reasons?
6
Characterization of Kleisli adjunctions
6
Axiom of Replacement in Category Theory
6
Can we define geometric morphisms (between ETCS categories) elementarily?
5
“classes” with no cardinality; “classes” with no equality notion
5
Are the axioms for higher category-theory effectively computable?
5
Joins of simplicial sets
5
Decomposing a large colimit as a pushout of smaller colimits
5
Probably easy: Why is f*:A^C'->A^C continuous and cocontinuous for any functor f:C->C'?
4
Describing global sections of sheafifications
4
Deformations and the dual numbers
4
Can we prove set theory is consistent?
4
Is it true that a set is countable if and only if there exists a Turing machine to enumerate all the elements in the set?
4
Game involving ‘asking questions about a real’
4
Left/right exact functor “in nature” which is not a right/left adjoint
3
Does this concept have a name, and what are some of its applications?
3
What happens when we print the digits of a real number?
3
An elementary question about adjunctions between presheaf categories preserving pullbacks.
3
A functor that comes from a morphism in a bigger category
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