User k.stm

24 votes

8 answers

16k views

How to interpret material conditional and explain it to freshmen?

asked Nov 7, 2012 at 18:29

16 votes

3 answers

6k views

Taylor expansion of $(1+x)^α$ to binomial series – why does the remainder term converge?

asked May 26, 2013 at 15:05

15 votes

3 answers

366 views

Embeddings $A → B → A$, but $A \not\cong B$?

asked May 20, 2014 at 20:16

12 votes

2 answers

1k views

Are the polynomial functions on $S^1$ dense in $C(S^1,ℂ)$?

asked Dec 14, 2014 at 16:08

12 votes

1 answer

3k views

Example of a non-splitting exact sequence $0 → M → M\oplus N → N → 0$

asked Dec 27, 2014 at 10:36

10 votes

1 answer

671 views

How is induction justified in intuitionistic logic?

asked Jan 26, 2015 at 23:25

9 votes

1 answer

127 views

Is there some sort of trick to show naturality?

asked Nov 9, 2015 at 21:32

7 votes

1 answer

183 views

Are there integral domains of dimension two with exactly four primes? How do they look like?

asked May 24, 2017 at 23:03

7 votes

2 answers

300 views

Proving adjoint functors preserve limits by lifting the adjunction to cone categories

asked Aug 1, 2017 at 7:13

7 votes

2 answers

1k views

troubles proving every subset of a finite set is finite with naive set theory

asked Nov 11, 2012 at 10:31

6 votes

2 answers

493 views

Is there a name for a monoid with a distinguished absorbing element?

asked Nov 7, 2015 at 11:05

6 votes

1 answer

391 views

Is this categorical definition of homology correct and, furthermore, used to teach homology in some book?

asked Jul 21, 2017 at 8:00

5 votes

2 answers

984 views

Can the cohomology ring of the two-fold torus be calculated abstractly?

asked Feb 2, 2015 at 18:52

5 votes

1 answer

916 views

Why are functors exact if they preserve all short exact sequences?

asked Apr 8, 2015 at 18:42

5 votes

1 answer

150 views

Introducing $\mathrm π$ and polar coordinates in real analysis

asked Jan 18, 2015 at 17:53

5 votes

0 answers

411 views

Why is this a characterization of isogenies of elliptic curves? (From Silverman)

asked Nov 20, 2012 at 11:32

5 votes

2 answers

775 views

Elliptic Points of Modular Group in Upper Half Plane

asked Sep 30, 2012 at 13:55

5 votes

1 answer

47 views

Is a set open in a product of spaces if all its segments are open in their factors?

asked Nov 6, 2014 at 7:11

5 votes

0 answers

606 views

Does every smooth surjective function have a smooth right inverse?

asked May 14, 2013 at 13:50

5 votes

1 answer

3k views

Is every left maximal ideal the annihilator of a simple left module?

asked Mar 18, 2014 at 10:48

5 votes

0 answers

150 views

What does an additive, mono-preserving functor have to do to become left exact?

asked Nov 22, 2017 at 8:19

5 votes

1 answer

137 views

Finding a lower bound on possible derivations for a contradiction within a theory like Zermelo–Fraenkel set theory

asked Jul 13, 2020 at 11:19

4 votes

2 answers

133 views

Are inversion and multiplicaton open?

asked Oct 3, 2012 at 9:43

4 votes

1 answer

667 views

Visualizing Infinity discerning countable and uncountable

asked Sep 23, 2012 at 16:01

4 votes

3 answers

149 views

Is there a sequence whose arithmetic means lie dense in $[-1..1]$?

asked Jan 21, 2013 at 17:48

4 votes

0 answers

127 views

Connected spaces where all subsets are either open or closed

asked May 7, 2015 at 6:21

4 votes

3 answers

339 views

Is reduced homology a full functor on connected spaces?

asked Jan 29, 2015 at 19:30

4 votes

1 answer

326 views

Neukirch’s Number Theory – why is $ℂ \otimes_ℚ K → K_ℂ,~z \otimes a ↦ (j(z)a)_τ$ an isomorphism?

asked Dec 24, 2016 at 11:20

4 votes

2 answers

1k views

What does the theory of the empty set look like?

asked Dec 11, 2015 at 15:14

4 votes

1 answer

105 views

A good book on humankind’s understanding of primes?

asked Jun 21, 2015 at 20:45

Stack Exchange Network

77 Questions

How to interpret material conditional and explain it to freshmen?

Taylor expansion of $(1+x)^α$ to binomial series – why does the remainder term converge?

Embeddings $A → B → A$, but $A \not\cong B$?

Are the polynomial functions on $S^1$ dense in $C(S^1,ℂ)$?

Example of a non-splitting exact sequence $0 → M → M\oplus N → N → 0$

How is induction justified in intuitionistic logic?

Is there some sort of trick to show naturality?

Are there integral domains of dimension two with exactly four primes? How do they look like?

Proving adjoint functors preserve limits by lifting the adjunction to cone categories

troubles proving every subset of a finite set is finite with naive set theory

Is there a name for a monoid with a distinguished absorbing element?

Is this categorical definition of homology correct and, furthermore, used to teach homology in some book?

Can the cohomology ring of the two-fold torus be calculated abstractly?

Why are functors exact if they preserve all short exact sequences?

Introducing $\mathrm π$ and polar coordinates in real analysis

Why is this a characterization of isogenies of elliptic curves? (From Silverman)

Elliptic Points of Modular Group in Upper Half Plane

Is a set open in a product of spaces if all its segments are open in their factors?

Does every smooth surjective function have a smooth right inverse?

Is every left maximal ideal the annihilator of a simple left module?

What does an additive, mono-preserving functor have to do to become left exact?

Finding a lower bound on possible derivations for a contradiction within a theory like Zermelo–Fraenkel set theory

Are inversion and multiplicaton open?

Visualizing Infinity discerning countable and uncountable

Is there a sequence whose arithmetic means lie dense in $[-1..1]$?

Connected spaces where all subsets are either open or closed

Is reduced homology a full functor on connected spaces?

Neukirch’s Number Theory – why is $ℂ \otimes_ℚ K → K_ℂ,~z \otimes a ↦ (j(z)a)_τ$ an isomorphism?

What does the theory of the empty set look like?

A good book on humankind’s understanding of primes?