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location Berlin, Germany
age 26
visits member for 3 years, 6 months
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I got my Master degree in Pure Mathematics in Rome, and now I'm a PhD-student in Berlin.

My main research interest is Arithmetic Geometry, but I'm here mainly because I like to keep an open eye towards a variety of fields in Mathematics!


Jan
14
comment The lower bound on the number of numbers needed to fill a matrix in a special way.
This is wrong. Pick $n=2$, then...
Jan
14
comment Prove a function is primitive recursive
You are welcome! The problem with your solution seems to me that $f(x-a)$ could be not well defined. In the sense that a primitive recursive function goes from $\mathbb{N}$ to $\mathbb{N}$ and if $x<a$ then $x-a\notin\mathbb{N}$. Moreover you should observe that the composition of primitive recursive functions is primitive recursive. If you want to be sure to have understood a good exercise could be to write $f_n(x)=x+n$ only in terms of projective and successor functions. Lastly, do you know how to accept an answer?
Jan
14
answered Prove a function is primitive recursive
Jan
14
comment Prove a function is primitive recursive
Welcome to Math.SE! You could have considered the addition of this link to your question: en.wikipedia.org/wiki/Primitive_recursive_function . In specific the paragraph "Addition" in the page above should answer your question. Is it correct?
Jan
12
accepted Computation of a (probably) tricky limit.
Jan
10
comment Computation of a (probably) tricky limit.
@Marek Thank you very much! I unzipped your comment and you`re totally right (there is still a factor 2 missing, but I'm confident I'll find it once reviewing the computation)! If you want to put it as an answer I will accept and upvote it as soon as possible! :)
Jan
10
revised Computation of a (probably) tricky limit.
edited body
Jan
10
comment Evaluate a double infinite summation
Where does this problem come from? Are you familiar with the notion of Eisenstein series? en.wikipedia.org/wiki/Eisenstein_series It seems quite close to it. But I don't see straight away any explicit relation between the two. If you could provide some more details we could help you better.
Jan
10
comment Evaluate a double infinite summation
What is your question?
Jan
10
comment What is $\operatorname{Ext}_{\mathbb{Z}} (\mathbb{Z}/m\mathbb{Z},\mathbb{Z}/n\mathbb{Z})$?
Are you looking at $\mathbb{Z}/m\mathbb{Z}$ and $\mathbb{Z}/n\mathbb{Z}$ as $\mathbb{Z}$-modules?
Jan
10
revised Computation of a (probably) tricky limit.
added 10 characters in body
Jan
10
asked Computation of a (probably) tricky limit.
Dec
5
comment Sheaf of Ramification Divisor - Hurwitz Formula
The first claim I cited is in Row 2 of the Proof. The second is in Row 6.
Dec
5
comment Sheaf of Ramification Divisor - Hurwitz Formula
Ok, I see! Now I understand the question. :) It looks tough, because it seems to be in open contradiction with the claim he makes a few rows above and which I reported. I'm gonna think about it!
Dec
5
comment Sheaf of Ramification Divisor - Hurwitz Formula
I don't see where is he making such a claim. It looks that he claims $\mathcal{O}_R \simeq \Omega_{X/Y}$ and $f^*\Omega_Y \otimes \Omega_X^{-1} \simeq \mathcal{L}(-R)$. Am I missing something obvious?
Nov
26
comment Equivalence of definition for polarized K3
Thank you very much, now I see it! Unfortunately I didn't encounter the Lefschetz decomposition while googling around. I have a stupid follow up question: "Do all the polarizations of an algebraic K3 surface arise as intersection pairing with signs changed?". On one hand I would say no, because there are polarizable non-algebraic K3s. But on the other hand this would contradict the choice of a polarized algebraic K3 as a pair $(X,\omega)$ for $\omega$ ample. Again I'm a bit confused. Thank you! :)
Nov
26
accepted Equivalence of definition for polarized K3
Nov
26
revised Equivalence of definition for polarized K3
added 2 characters in body
Nov
26
asked Equivalence of definition for polarized K3
Nov
23
comment Problem on finding Geodesics on a surface
In your question there are two questions. What is the one which gives you troubles?