User fosco

68 votes

8 answers

4k views

A bestiary about adjunctions

asked Jun 21, 2011 at 14:42

39 votes

7 answers

9k views

Beautiful identity: $\sum_{k=m}^n (-1)^{k-m} \binom{k}{m} \binom{n}{k} = \delta_{mn}$

asked Sep 7, 2010 at 0:21

32 votes

6 answers

7k views

A non-noetherian ring with noetherian spectrum

asked Oct 21, 2010 at 8:56

31 votes

2 answers

1k views

The longest list of analogies between vector spaces and categories ever made

asked Nov 1, 2017 at 22:09

28 votes

2 answers

8k views

What is Mazzola's "Topos of Music" about?

asked May 4, 2012 at 19:18

24 votes

2 answers

2k views

Understanding Alexandroff compactification

asked Aug 26, 2012 at 11:44

18 votes

1 answer

595 views

Does every l.e.s. "in homology" come from a s.e.s. of complexes?

asked Dec 8, 2010 at 20:34

17 votes

3 answers

1k views

Theory of promonads

asked Apr 25, 2013 at 10:51

15 votes

2 answers

1k views

Is there an abelian category of topological groups?

asked Mar 31, 2012 at 10:53

14 votes

0 answers

298 views

Transfinite horizontal composition

asked Jun 11, 2013 at 11:39

12 votes

2 answers

347 views

Essential geometric morphism seen topologically

asked Mar 29, 2013 at 15:05

12 votes

2 answers

4k views

$\mathbb{Z}/2\mathbb{Z}$ coefficients in homology

asked Jun 23, 2011 at 8:14

11 votes

1 answer

786 views

Limits in the category of exact sequences

asked Oct 26, 2010 at 18:42

11 votes

0 answers

562 views

Are limits categorical limits? [duplicate]

asked Jan 15, 2012 at 15:51

10 votes

2 answers

3k views

Various definitions of group action

asked Jun 25, 2011 at 20:22

10 votes

2 answers

684 views

A suitable product of graphs

asked Sep 24, 2012 at 16:51

9 votes

2 answers

357 views

The homology of $\Omega T^n$

asked Aug 18, 2015 at 10:00

9 votes

2 answers

3k views

Quotient field of a quotient ring

asked Jan 23, 2011 at 13:35

9 votes

3 answers

401 views

A space whose powers "generate" all spaces via quotients

asked Jul 16, 2017 at 12:40

8 votes

2 answers

4k views

Direct sum of complexes

asked Dec 12, 2010 at 17:28

8 votes

2 answers

2k views

Derived functors are Kan extensions

asked Dec 27, 2011 at 17:37

7 votes

2 answers

532 views

"Change-of-base" between enriched categories

asked Jul 4, 2011 at 18:28

7 votes

1 answer

2k views

Proof that the Nijenhuis tensor vanishes in a complex manifold

asked Jul 22, 2011 at 10:27

7 votes

2 answers

294 views

Naturality can be detected on a dense subcategory

asked Jul 10, 2017 at 20:20

6 votes

1 answer

198 views

Does a geometric morphism $f\colon \cal E\to F$ preserves and reflects the subobject classifier?

asked Feb 27, 2012 at 20:08

6 votes

1 answer

505 views

Is the t-truncation a functor?

asked Aug 13, 2013 at 12:02

6 votes

1 answer

424 views

Does the comma category functor have an adjoint?

asked Sep 18, 2013 at 15:08

6 votes

0 answers

94 views

Fixed point of adjunctions

asked Nov 11, 2013 at 20:24

6 votes

2 answers

659 views

Associativity of Day convolution

asked Jan 30, 2013 at 20:23

5 votes

0 answers

171 views

A model structure on $\bf Cat$

asked Oct 20, 2012 at 14:59

Stack Exchange Network

93 Questions

A bestiary about adjunctions

Beautiful identity: $\sum_{k=m}^n (-1)^{k-m} \binom{k}{m} \binom{n}{k} = \delta_{mn}$

A non-noetherian ring with noetherian spectrum

The longest list of analogies between vector spaces and categories ever made

What is Mazzola's "Topos of Music" about?

Understanding Alexandroff compactification

Does every l.e.s. "in homology" come from a s.e.s. of complexes?

Theory of promonads

Is there an abelian category of topological groups?

Transfinite horizontal composition

Essential geometric morphism seen topologically

$\mathbb{Z}/2\mathbb{Z}$ coefficients in homology

Limits in the category of exact sequences

Are limits categorical limits? [duplicate]

Various definitions of group action

A suitable product of graphs

The homology of $\Omega T^n$

Quotient field of a quotient ring

A space whose powers "generate" all spaces via quotients

Direct sum of complexes

Derived functors are Kan extensions

"Change-of-base" between enriched categories

Proof that the Nijenhuis tensor vanishes in a complex manifold

Naturality can be detected on a dense subcategory

Does a geometric morphism $f\colon \cal E\to F$ preserves and reflects the subobject classifier?

Is the t-truncation a functor?

Does the comma category functor have an adjoint?

Fixed point of adjunctions

Associativity of Day convolution

A model structure on $\bf Cat$