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Peter Smith
  • Member for 10 years, 1 month
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37 votes
3 answers
2k views

Simple/natural questions in group theory whose answers depend on set theory

26 votes
5 answers
2k views

Alternative set theories

18 votes
1 answer
900 views

Primitive recursive function which isn't $\Delta_0$

17 votes
2 answers
437 views

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

17 votes
2 answers
935 views

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

17 votes
2 answers
695 views

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

16 votes
2 answers
330 views

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

16 votes
3 answers
2k views

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

16 votes
1 answer
633 views

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

13 votes
1 answer
282 views

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

12 votes
1 answer
539 views

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

11 votes
0 answers
236 views

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

10 votes
1 answer
208 views

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

9 votes
1 answer
513 views

Do hom-sets really live in the category Set?

8 votes
1 answer
233 views

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

8 votes
1 answer
673 views

Introductions to intuitionistic logic?

7 votes
1 answer
139 views

Survey of varieties of non-standard analysis?

7 votes
1 answer
843 views

Symbol for assignment of a truth-value?

7 votes
1 answer
271 views

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

7 votes
1 answer
507 views

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

6 votes
2 answers
358 views

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

6 votes
3 answers
137 views

Categories with some but not all exponentials

5 votes
2 answers
678 views

A proof that right adjoints preserve limits?

5 votes
0 answers
207 views

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

4 votes
2 answers
1k views

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

4 votes
0 answers
81 views

Symbol for function composition [duplicate]

4 votes
0 answers
173 views

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

4 votes
3 answers
243 views

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

4 votes
1 answer
170 views

Mathematicians endorsing platonism -- examples?

3 votes
0 answers
39 views

Replacement and implementation-independence in set theory