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dfeuer
  • Member for 12 years, 7 months
  • Last seen more than a week ago
52 votes

Why is empty set an open set?

22 votes

Matrix Algebra Question (Linear Algebra)

18 votes

Why does factoring eliminate a hole in the limit?

15 votes

How can I show that a sequence of regular polygons with $n$ sides becomes more and more like a circle as $n \to \infty$?

12 votes
Accepted

nitpicking the definition of a polynomial function

11 votes

Mathematical writing: why should we not use the phrase "we have that"?

10 votes
Accepted

What is the difference between a ball and a neighbourhood?

9 votes
Accepted

What does $X \subsetneqq Y$ mean

9 votes
Accepted

The probability that two vectors are linearly independent.

9 votes

Proving that the union of the limit points of sets is equal to the limit points of the union of the sets

8 votes

Isn't codomain of a function ambiguous?

8 votes

Prove that $6$ divides $n(n + 1)(n + 2)$

8 votes

Why is compactness so important?

7 votes
Accepted

Showing $\mathbb{R}/\mathbb{Q}$ is not Hausdorff

7 votes

How can one prove that $e<\pi$?

7 votes
Accepted

If $f:\mathbb{R}^n \to \mathbb{R}^n$ is continuous with convex image, and locally 1-1, must it be globally 1-1?

7 votes

Covering for connected and locally path connected spaces

6 votes

Closure in box and product topology

6 votes

Fibered products in $\mathsf {Set}$

6 votes
Accepted

What is the simplest mathematical concept that does not map to a physical phenomenon?

6 votes
Accepted

The principle of duality for sets

6 votes
Accepted

Accumulation Points & Convergence: A Sequence Existence Proof

6 votes

What precisely is lost when considering proper classes rather than sets?

6 votes
Accepted

Is this graph a planar graph?

5 votes
Accepted

Each component of $X$ is second-countable

5 votes

If we abandon the axiom of regularity, can the cumulative hierarchy just become a definition?

5 votes

How do I know when to use nCr button and when to use nPr button on my calculator in which situation?

5 votes
Accepted

Does $a_n = \cos\left(n\ln \left(1+\frac{\pi}{n}\right)\right)$ converge?

5 votes
Accepted

How can you use a (fair) coin to draw straws among 3 people? (Information Theory)

5 votes

Intersection of Closed and Compact Set is Closed

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