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I'm a student of mathematics in Germany.


5h
comment How can I show that the tensor product of $\mathbb Z$ and $\mathbb R$ as $\mathbb Z$ modules is isomorphic to $\mathbb C$?
Uh, I was like “How can be ℂ, it’s ℝ!” – kind of a trick question, I guess.
Sep
7
comment Why is multiplication commutative - intuitive explanation
How about viewing the product $a·b$ as calculating the area of a rectangle with corresponding side lengths $a$ and $b$, and then viewing commutativity $a·b = b·a$ in that context as the fact that its area doesn’t change with a reflection of the rectangle?
Aug
30
comment Why $|G|$ even implies $|A(G)|$ also even?
@PtF Yeah, but that’d be a circular argument. It directly follows for any finite group $G$ that $A(G)$ has an even number of elements. The second statement is just a corollary and doesn’t have to be used (nor should it be) to again show that $|A(G)|$ is even.
Aug
25
comment How to proof homeomorphism between open ball and normic space
@MathewGeorge Both the function and its inverse are mentioned in the post – what do you mean?
Aug
22
comment Exercise on characterization of free abelian groups
@user113913 In that case you may also be interested in replacing the image-argument you have given to prove $f$ is epic by directly proving that both constructed arrows $f$, and the other $G → F$ are in fact inverse to each other. That would be bit more category-theoretic in flavour. (Your argument is of course perfectly fine, though.)
Aug
22
answered Exercise on characterization of free abelian groups
Aug
22
comment Exercise on characterization of free abelian groups
What is $ϕ$, though? Did you maybe mix up your names in the middle ant $ϕ$ is really $f$ and $f$ is really $h$?
Aug
13
revised How can I find $\mathbb Z_4$ as an extension of $\mathbb Z_2$ by $\mathbb Z_2$?
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Aug
13
revised How can I find $\mathbb Z_4$ as an extension of $\mathbb Z_2$ by $\mathbb Z_2$?
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Aug
13
revised How can I find $\mathbb Z_4$ as an extension of $\mathbb Z_2$ by $\mathbb Z_2$?
fixed definition of π
Aug
13
revised How can I find $\mathbb Z_4$ as an extension of $\mathbb Z_2$ by $\mathbb Z_2$?
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Aug
13
answered How can I find $\mathbb Z_4$ as an extension of $\mathbb Z_2$ by $\mathbb Z_2$?
Aug
13
comment How can I find $\mathbb Z_4$ as an extension of $\mathbb Z_2$ by $\mathbb Z_2$?
Do I understand you correctly in that you want to know how to construct a group extension from a $2$-cocycle?
Aug
13
comment How can I find $\mathbb Z_4$ as an extension of $\mathbb Z_2$ by $\mathbb Z_2$?
What is $FS$ and $IFS$?
Aug
12
comment Understanding the proof of: If $|A| = \kappa$, then $|\mathcal{P}(A)|=2^{\kappa}$.
I wouldn’t call it a mistake. I think the author uses “$f\colon X → χ_X$” for “$f\colon X ↦ χ_X$”.
Aug
11
comment If $\sum a_n$ converges and $b_n=\sum\limits_{k=n}^{\infty}a_n $, prove that $\sum \frac{a_n}{b_n}$ diverges
Is this homework, though?
Jul
20
comment Are there any well known mathematicians who published very little?
I don’t know how much Hermann Grassmann published, but he might be a candidate: I believe he is only known for his Lineare Ausdehnungslehre in which he conceived of linear and multilinear algebra (including the exterior product).
Jul
2
awarded  Curious
Jul
1
comment How to proof (using by mathematical induction)($n\in \mathbb{N}$)
@user159813 $\frac 1 n \overset{n → ∞} \longrightarrow 0$, but $\frac 1 n > 0$, so $0 > 0$?
Jun
30
comment If $AB = I$ then $BA = I$: is my proof right?
It’s not correct – see Thomas’ comment. And @agha: I think she or he is more interested in finding an own proof.