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tomasz
  • Member for 10 years, 2 months
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107 votes

Why is radian so common in maths?

51 votes

Are there mathematical concepts that exist in dimension $4$, but not in dimension $3$?

42 votes

Difference between closed, bounded and compact sets

37 votes
Accepted

Is there an example of an ordered ring that is not isomorphic to any subring of the real numbers?

33 votes
Accepted

Is it necessary for one to understand analysis?

31 votes
Accepted

How to show $i^{-1} = -i$?

31 votes

How to learn from proofs?

29 votes

On "familiarity" (or How to avoid "going down the Math Rabbit Hole"?)

27 votes
Accepted

Showing that projections $\mathbb{R}^2 \to \mathbb{R}$ are not closed

23 votes

The Euler characteristic of S1: a paradox

23 votes

Are the only sets in $\mathbb{R^1}$ which are both open and closed $\mathbb{R^1}$ and $\emptyset$?

21 votes

Visualizing quotient groups: $\mathbb{R/Q}$

19 votes
Accepted

Example when the torsion of a module is not a submodule.

19 votes

Galois Field GF(4)

18 votes

If $f: \mathbb Q\to \mathbb Q$ is a homomorphism, prove that $f(x)=0$ for all $x\in\mathbb Q$ or $f(x)=x$ for all $x$ in $\mathbb Q$.

17 votes
Accepted

Does the union of two not disjoint open balls always contain the line connecting the two centers?

16 votes
Accepted

Is there an uncountable proper sub-field of $\mathbf{R}$?

16 votes

Why do we use trig functions in Fourier transforms, and not other periodic functions?

15 votes

Is $[0,1] \cap \Bbb Q$ a compact subset of $\Bbb Q$?

15 votes

How to construct a Bernstein set and what are their applications?

14 votes
Accepted

What is the motivation for differential forms?

14 votes

subset of binary space countable?

13 votes
Accepted

How to think of the field $F(\alpha)$

12 votes
Accepted

Topological manifolds (dimension)

11 votes
Accepted

Why metrizable group requires continuity of inverse?

11 votes
Accepted

Every point closed $\stackrel{?}{\Rightarrow}$ space is Hausdorff

10 votes
Accepted

Infinitely many axioms of ZFC vs. finitely many axioms of NBG

10 votes

What does $C^{\infty}_0$ stand for

10 votes

What is an irreducible character of a finite group?

10 votes
Accepted

Why do mathematicians use this symbol $\mathbb R$ to represent the real numbers?

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