299

Answers

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9

Proof by contradiction in a topos

7

For a monoid with zero $M$, how many additive operations on $M$ can there be making $M$ a ring?

14

Elementary proof for identity involving sums of binomials

5

Is there any nontrivial monad on the category of graphs?

5

What is “Data” involved in a mathematical construction?

5

Does “induction” for a functor algebra imply it is initial?

4

Fixed point theorems

11

How to refer to a theorem that you have shown to be wrong

4

Which compositions have these sum-like and product-like properties on the positive reals?

2

Sums of Squares and Totally Positive Numbers

6

How to show a certain determinant is non-zero

5

On the category of virtual species

2

Bases of open sets with connected intersections

10

Is there a constructive proof of Cantor–Bernstein–Schroeder theorem ?

3

Are exponentials in categorical models of linear logic harmful?

1

Gödel, Escher, Bach: b is a power of 10.

4

Products of Boolean algebras and probability measures thereon

8

Reference for my monads?

1

Flatness of projective bundles

2

Unitalization internal to monoidal categories

4

What is a good example of a hyperspace where the base space is non-Hausdorff?

7

Adjoint of Pushout as Modal Operators in Internal Logic

13

Where in ordinary math do we need unbounded separation and replacement?

3

Trichotomies in mathematics

21

Is the empty graph a tree?

15

Noncontractible connected topological rings ?

16

Unit sphere in R^\infty is contractible?

9

Vertical and Horizontal Isomorphisms in 2-categories

9

What, precisely, does Klein’s Erlangen Program state?

7

Free cocommutative commutative Hopf monoids