Daniel Donnelly's user avatar
Daniel Donnelly's user avatar
Daniel Donnelly's user avatar
Daniel Donnelly
  • Member for 11 years, 11 months
  • Last seen this week
45 votes

What is integration by parts, really?

19 votes
Accepted

$\partial (A \cap B) = \partial A \cap \partial B $?

9 votes

Proof of Yoneda Lemma

8 votes

Unorthodox way of getting the average of two numbers

7 votes
Accepted

Learning to understand proofs faster?

7 votes

Sum of two maximal ideal is necesarily maximal ideal?

7 votes
Accepted

How do you show that $f(x) = e^{-x^2}$ is in the Schwartz space $\mathcal{S}(\Bbb{R})$?

6 votes
Accepted

Matrix representation of Automata

6 votes

Why a subspace of a vector space is useful

5 votes

How to show that there is no $3\times3$ real matrix $A$ such that $A^2+I=0$?

5 votes

Proving a metric induces the product topology

5 votes

The Category of Small Categories: a Zoo of Functors.

5 votes

show that torus is compact

5 votes

$\Bbb{Z}/p^k \Bbb{Z} \otimes_{\Bbb{Z}} A $ is isomorphic to the Sylow $p$-subgroup of $A$

5 votes

When is the product of two quotient maps a quotient map?

5 votes
Accepted

How could I understand this sentence:

5 votes

List of small rings

4 votes

References to supplement Goldblatt's "Topoi"

4 votes
Accepted

Is "reverse homology" $\ker g \subset \text{im} f$ possible?

4 votes

path connected subspaces of $\mathbb R^2$

4 votes
Accepted

When do you use the internal vs. external direct sum of groups?

4 votes

How to prove surjectivity part of Short Five Lemma for short exact sequences.

4 votes

Proof of geometric congruence using linear algebra

4 votes
Accepted

What is the purpose of sets? Why do we use them?

4 votes

Integrality Conjectures

4 votes
Accepted

Is the center of a ring an ideal?

4 votes

Unions of families

4 votes

If $Y$ is an irreducible subset of $X$, then its closure $\overline{Y}$ in $X$ is also irreducible.

4 votes

Can someone confirm this set does not form a group

3 votes

How to show that if a 3x3 matrix A and it's diagonal B are in SO(3) that their product is in SO(3)

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