4,428 reputation
1723
bio website
location
age
visits member for 2 years, 3 months
seen 3 hours ago

I'm a student of mathematics in Germany.


Dec
13
answered How to figure out Laurent series expansion for $z^2 \sin(1/(z+i))$?
Dec
13
reviewed Approve Calculate: $ \lim_{x \to 0 } = x \cdot \sin(\frac{1}{x}) $
Dec
13
reviewed Approve I can't solve this limit without using L'Hospital
Dec
13
comment How to figure out Laurent series expansion for $z^2 \sin(1/(z+i))$?
Around which point, $-i$?
Dec
13
reviewed Approve How to figure out Laurent series expansion for $z^2 \sin(1/(z+i))$?
Dec
13
answered Several questions on the mean value theorem?
Dec
13
comment A wheel with $n$ is not homeomorphic to a wheel with $m$ spokes
I don’t know how much effort it will be to do the formal work, but if you remove the center from any (small enough) neighbourhood of the center of $W_n$, you get $n$ connected components in that neighbourhood (the spikes, of course). If $n > m$, this won’t be possible for $W_m$.
Dec
13
comment Ring whose all ideals are double-sided is commutative?
@Mike $D × 0$ is a two-sided ideal in $D × D$ for any division ring $D$, like that?
Dec
13
comment Ring whose all ideals are double-sided is commutative?
@Mike In finite products of division rings, there are nontrivial ideals. They’re just a bit boring as well.
Dec
13
comment Show the intersection of a nonidentity normal subgroup and the center of P is not trivial
What do you mean by “nontrivial union”?
Dec
13
answered Ring whose all ideals are double-sided is commutative?
Dec
13
comment Boundary of Boundary of a set?
How about singletons in $ℝ$?
Dec
12
comment Is there an easy way to remember the ring axioms?
Have you tried remembering them by their names?
Dec
12
revised Notation $x^n=(x_1,\dotsc,x_n)$
edited tags
Dec
12
comment Noetherian ring not descending chain condition
Did you mean for “$Z$” (or “$\Z$”) to denote the ring of integers $ℤ$? (If so you shouldn’t write “Let $Z$ be a ring …”, but “Let $ℤ$ be the ring of integers.”) Maybe you should get more specific and really use integers like $2, 4, …$ for your proof.
Dec
12
revised Noetherian ring not descending chain condition
replaced non-working tex-code
Dec
11
comment What ring is isomorphic to factor-ring?
This will not be $ℝ$ – there are only countably many polynomials in $R = ℤ[X]$, so there are only countably many elements in $R/I$.
Dec
11
awarded  Custodian
Dec
11
reviewed Close Algorithm to numerically solve this system of three polynomial equations of degree $6$
Dec
11
revised Let $R=M_n(D)$, $D$ is a division ring. Prove that every $R-$simple module is isomorphic to each other.
minor correction