User Peter Smith

10

24

votes

5

answers

1k

views

Alternative set theories

May 28 '18 at 4:33 Martin Sleziak 47k

7

17

votes

2

answers

589

views

You've got your head round Basic Category Theory: why look at monads next?

reference-request soft-question category-theory

Nov 12 '15 at 18:30 Community♦ 1

6

16

votes

2

answers

625

views

The (un)decidability of Robinson-Arithmetic-without-Multiplication?

logic

Oct 30 '14 at 19:58 Henning Makholm 257k

5

16

votes

1

answer

557

views

Primitive recursive function which isn't $\Delta_0$

logic computability recursion

Apr 17 '13 at 17:33 Carl Mummert 69.5k

3

16

votes

1

answer

561

views

Mendelson's $\mathit{Mathematical\ Logic}$ and the missing Appendix on the consistency of PA

reference-request logic math-history

Feb 15 '13 at 19:38 Peter Smith 41.6k

1

15

votes

2

answers

274

views

Natural isomorphisms: what is the status now of “the Eilenberg/Mac Lane Thesis”?

category-theory soft-question natural-transformations

Oct 16 at 11:03 Peter Smith 41.6k

3

14

votes

2

answers

376

views

Two styles of semantics for a first-order language: what's to choose?

logic predicate-logic

Sep 2 '13 at 10:26 Carl Mummert 69.5k

2

12

votes

1

answer

224

views

Is there a quicker argument from the HBL derivability conditions to the equivalence of fixed points of $\neg\Box$ to $\mathsf{Con}$?

logic incompleteness

Jul 22 '16 at 2:51 Henning Makholm 257k

4

12

votes

3

answers

1k

views

What's a good motivating example for the concept of a slice category?

category-theory intuition examples-counterexamples big-list motivation

Sep 13 '15 at 16:48 Alex Kruckman 32.6k

5

11

votes

0

answers

209

views

Elementary references on Robinson Arithmetic, Prim. Recursive fns etc.

reference-request logic computability incompleteness arithmetic-functions

Jan 28 '14 at 20:03 Peter Smith 41.6k

5

10

votes

0

answers

447

views

Olympiad-style question about functions satisfying condition $f(f(f(n))) = f(n+1) + 1$

elementary-number-theory functions

Jan 27 '15 at 20:48 Peter Smith 41.6k

1

10

votes

1

answer

199

views

Who first explicitly noted that second-order logic is unaxiomatizable?

logic math-history

Nov 22 '12 at 16:13 Carl Mummert 69.5k

3

9

votes

1

answer

166

views

What is a nice “naturally occurring” example of an arrow category?

category-theory

Nov 30 '15 at 15:06 goblin 38.3k

7

8

votes

1

answer

315

views

Do hom-sets really live in the category Set?

reference-request soft-question category-theory

Apr 8 '15 at 4:27 Community♦ 1

1

7

votes

1

answer

404

views

Symbol for assignment of a truth-value?

logic notation

Jan 14 '18 at 9:12 Peter Smith 41.6k

2

7

votes

1

answer

122

views

Survey of varieties of non-standard analysis?

reference-request nonstandard-analysis

Mar 16 '17 at 13:47 Community♦ 1

2

6

votes

1

answer

144

views

Recent sets of notes/newly available online books on category theory?

reference-request category-theory self-learning online-resources

Feb 25 '18 at 16:05 Martin Sleziak 47k

2

6

votes

2

answers

237

views

Examples of functors that preserves products but not equalizers, and vice versa.

soft-question category-theory

Mar 26 '15 at 0:12 Andreas Blass 53.6k

2

5

votes

2

answers

438

views

A proof that right adjoints preserve limits?

category-theory limits-colimits adjoint-functors

Jan 13 '16 at 20:11 Najib Idrissi 43.7k

2

5

votes

3

answers

113

views

Categories with some but not all exponentials

category-theory examples-counterexamples

Sep 6 '15 at 21:36 Community♦ 1

1

5

votes

1

answer

236

views

How to prove adjunctions compose (via units and counits)?

category-theory

Jun 6 '15 at 22:02 Rolf Hoyer 11.5k

1

5

votes

0

answers

179

views

The counted is to the countable as the ??? is to the (order)-isomorphic.

elementary-set-theory terminology

Aug 23 '13 at 19:46 Community♦ 1

1

4

votes

0

answers

70

views

Symbol for function composition [duplicate]

functions notation math-history

Jan 26 '13 at 8:54 Community♦ 1

1

4

votes

0

answers

166

views

Cutest proof that PA proves its finitely axiomatised subtheories are consistent?

reference-request logic

Aug 4 '12 at 8:18 Peter Smith 41.6k

3

votes

3

answers

129

views

Free variables, parameters, dummy names — what policy to choose?

logic quantifiers

Mar 16 '18 at 17:37 Peter Smith 41.6k

3

votes

2

answers

636

views

Introductory example(s) of a functor that is full but not faithful

category-theory examples-counterexamples big-list

Oct 21 '14 at 5:25 Peter Smith 41.6k

3

votes

1

answer

87

views

A query about countability

analysis elementary-set-theory logic

Sep 28 '13 at 0:59 Trevor Wilson 15k

3

votes

2

answers

115

views

Notation for function that returns exponent of primes in factorisation?

elementary-number-theory terminology

Jul 20 '12 at 23:54 André Nicolas 461k

1

2

votes

3

answers

147

views

When we talk of e.g. the natural numbers equipped with a non-standard order , what does “equipped” mean?

terminology order-theory

Jul 8 '14 at 14:47 Mauro ALLEGRANZA 72.1k

2

1

vote

1

answer

134

views

Functors from $\mathsf{Set}$ to $\mathsf{Mon}$?

category-theory

Sep 28 '15 at 21:25 Qiaochu Yuan 290k

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31 Questions

Alternative set theories

You've got your head round Basic Category Theory: why look at monads next?

The (un)decidability of Robinson-Arithmetic-without-Multiplication?

Primitive recursive function which isn't $\Delta_0$

Mendelson's $\mathit{Mathematical\ Logic}$ and the missing Appendix on the consistency of PA

Natural isomorphisms: what is the status now of “the Eilenberg/Mac Lane Thesis”?

Two styles of semantics for a first-order language: what's to choose?

Is there a quicker argument from the HBL derivability conditions to the equivalence of fixed points of $\neg\Box$ to $\mathsf{Con}$?

What's a good motivating example for the concept of a slice category?

Elementary references on Robinson Arithmetic, Prim. Recursive fns etc.

Olympiad-style question about functions satisfying condition $f(f(f(n))) = f(n+1) + 1$

Who first explicitly noted that second-order logic is unaxiomatizable?

What is a nice “naturally occurring” example of an arrow category?

Do hom-sets really live in the category Set?

Symbol for assignment of a truth-value?

Survey of varieties of non-standard analysis?

Recent sets of notes/newly available online books on category theory?

Examples of functors that preserves products but not equalizers, and vice versa.

A proof that right adjoints preserve limits?

Categories with some but not all exponentials

How to prove adjunctions compose (via units and counits)?

The counted is to the countable as the ??? is to the (order)-isomorphic.

Symbol for function composition [duplicate]

Cutest proof that PA proves its finitely axiomatised subtheories are consistent?

Free variables, parameters, dummy names — what policy to choose?

Introductory example(s) of a functor that is full but not faithful

A query about countability

Notation for function that returns exponent of primes in factorisation?

When we talk of e.g. the natural numbers equipped with a non-standard order , what does “equipped” mean?

Functors from $\mathsf{Set}$ to $\mathsf{Mon}$?