Gregor Bruns
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 Dec5 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. Dec4 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. Dec3 comment Conceptual question about equivalence of eigenvectors Yes. The eigenvalue doesn't even need to be $1$. Dec2 answered Are rings with the same finite cardinality isomorphic? Dec2 comment Proving that an equation has no natural solutions Wow, this is really clever! Nov30 comment A set of objects that satisfy $a^2 = \alpha x$ and commute Did you mean to write "with generators $\{x\}\cup Y$"? Nov30 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. Nov29 answered Associated points of a scheme are contained in an open subset Nov25 answered Schemes covered by finitely-many affine open subsets Nov25 comment Schemes covered by finitely-many affine open subsets I see you already found this thread. Just thought to link it here. Nov23 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 $10$. Nov23 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'? Nov22 accepted Closed points of a scheme correspond to maximal ideals in the affines? Nov22 comment Complex variables/analysis integration Did you try a substitution $u = tc/x$? Afterwards, you can recognize the integrand as the derivative of $\arctan(u)$. Nov21 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. Nov21 answered How to show that a form on $\mathbb{C}$ defines a holomorphic $1$-form on $\mathbb{C}/\Gamma$? Nov21 revised Closed points of a scheme correspond to maximal ideals in the affines? more concrete description of the problem Nov21 accepted Reading circle in mathematics? Nov21 asked Closed points of a scheme correspond to maximal ideals in the affines? Nov20 comment Generators of a finitely generated free module over a commutative ring @MakotoKato, I'm not so sure if the uniqueness of rank for commutative rings can be proved without choice. The proof I know uses it. So it may not be a drawback here.