# All Questions

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### Lie Algebras: (ad $\ y)^4(z)=0$, since root strings have length at most 4

Can somebody please explain this to me? (ad $\ y)^4(z)=0$, since root strings have length at most 4. Note: y and z are root vectors belonging to two negative roots.
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### How could contour integration be represented as a number?

What is a contour integral? In what ways can contour integration be represented as a number?
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Suppose i have Two Text Articles (article 'a' => x words, article 'b' => y words) i find the total number of words in 'a' = x the total number of occurances of the word "the" in the article = x1 ...
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### In what generality is the natural map $\textrm{Hom}_R(L,M)\otimes S \to \operatorname{Hom}_{R \otimes S}(L\otimes S, M \otimes S)$ an isomorphism?

Note: A version of this question has been reposted to MathOverflow. Let $k$ be a commutative ring, $R$ and $S$ commutative $k$-algebras. Let $L$ and $M$ be $R$-modules. Unless I am much mistaken, ...
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### Always solving systems of linear equations wrong - what do I do wrong?

Dear ladies and gentlemen, over time I noticed I (and other) again and again have problems solving "systems of linear equations". It seems depending of the steps one chooses, we get different ...
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### Possibilistic clustering- what exectly is $\eta$ and how to calculate it

I'm curently studing the topic of Possibilistic shell clustering and I have a hard time with understanding the concept of variable $\eta$. Can somebody in simpe words explain me what exectly this ...