Gregor Bruns
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 Dec 10 answered Find a normal extension over $\mathbb{Q}$ of degree 3 Dec 8 answered non-symmetric positive definite matrix!? Dec 5 comment Is it true that if a graph is n-regular that it must have n+1 vertices? I interpreted that as 'exactly', but you're right, maybe it was meant as 'at least'. Curiously, I didn't consider this, even if I used to draw two cards when someone told me to "Draw one card". Dec 5 comment Is it true that if a graph is n-regular that it must have n+1 vertices? No, it's not true. Google images for "3-regular graph" shows many counterexamples. A very famous one is the Petersen graph. Dec 4 comment Is $\mathbb R^2$ a field? Indeed, every finite-dimensional vector space $V$ over a field $\mathbb{F}$ is isomorphic to $\mathbb{F}^n$, where $n$ is the dimension of $V$. This fact impressed me a lot when I first learned it. Dec 3 comment Conceptual question about equivalence of eigenvectors Yes. The eigenvalue doesn't even need to be $1$. Dec 2 answered Are rings with the same finite cardinality isomorphic? Dec 2 comment Proving that an equation has no natural solutions Wow, this is really clever! Nov 30 comment A set of objects that satisfy $a^2 = \alpha x$ and commute Did you mean to write "with generators $\{x\}\cup Y$"? Nov 30 comment Are CASs useful in mathematics? Sage has become a very good choice for many problems, being sometimes faster than all other packages. But it has neither the stability of Magma, nor the user-friendly functionality of, e.g., Mathematica. This may change in some years, of course. Nov 29 answered Associated points of a scheme are contained in an open subset Nov 25 answered Schemes covered by finitely-many affine open subsets Nov 25 comment Schemes covered by finitely-many affine open subsets I see you already found this thread. Just thought to link it here. Nov 23 comment reducing a number with fractions If you know how many Ns there are after the decimal point, you can just multiply with an appropriate power of $10$. Nov 23 comment Is mathematics the only language that is not subject of interpretation? There are, for instance, several flavors of formal logic. Do you count them as 'mathematics'? Nov 22 accepted Closed points of a scheme correspond to maximal ideals in the affines? Nov 22 comment Complex variables/analysis integration Did you try a substitution $u = tc/x$? Afterwards, you can recognize the integrand as the derivative of $\arctan(u)$. Nov 21 comment How to show that a form on $\mathbb{C}$ defines a holomorphic $1$-form on $\mathbb{C}/\Gamma$? Yes, that's what I thought the exercise was about :). Does this seem right to you? Your first comment does some kind of converse. Nov 21 answered How to show that a form on $\mathbb{C}$ defines a holomorphic $1$-form on $\mathbb{C}/\Gamma$? Nov 21 revised Closed points of a scheme correspond to maximal ideals in the affines? more concrete description of the problem