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Nov
15
revised Vakil's Foundations of Algebraic Geometry, Exercise 5.5.E
added 99 characters in body
Nov
15
answered Vakil's Foundations of Algebraic Geometry, Exercise 5.5.E
Nov
15
accepted Is there an extensive 'cheat sheet' for general topology questions?
Nov
15
asked Reading circle in mathematics?
Nov
15
awarded  Fanatic
Nov
14
comment Approximation of $e$ by a rational number
Yes, you can. Do you need to give such a number? Do you know about continued fractions?
Nov
7
comment Common sense in mathematics
What do you mean by "mathematical method"? Does it include, e.g., finger counting? Where do "mathematical results" start for you?
Oct
20
comment Does Pi contain all possible number combinations?
You should probably do it in the order of ascending length, not in alphabetical order, because you would never get beyond the sentences starting with 'A'.
Oct
20
asked Was there a culture/number system with negative numbers but without zero?
Oct
19
comment An 'easy' way to prove that epimorphism of sheaves implies surjectivity on stalks
@ZhenLin: Thanks for your comment. I guess the general nonsense will have to do it for an elegant solution. It is not so difficult as I thought at first. If I want to have it more explicit, the longer solutions will still make visible where the surjectivity comes from.
Oct
19
asked Is there an extensive 'cheat sheet' for general topology questions?
Oct
1
awarded  Citizen Patrol
Oct
1
asked An 'easy' way to prove that epimorphism of sheaves implies surjectivity on stalks
Oct
1
comment Does every prime ideal in a ring arise as kernel of a homomorphism into $\mathbb{Z}$?
Only a minor comment: The first two sentences being in the same line makes them seem related, but they are not. Do you mind separating them (e.g. by an 'or')?
Sep
25
comment proof of chinese remainder theorem for ring
Let $a_i + b_j = 1$. Multiply both sides by $x$, you get $xa_i+xb_j=x$. Now $xa_i$ is in $I$ and $xb_j$ is in $J$, because $I$ and $J$ are ideals. That is, for every $x\in R$ you get $x_i\in I$ and $x_j\in J$ such that $x_i+x_j=x$.
Sep
25
answered proof of chinese remainder theorem for ring
Sep
21
comment What is $dx$ in integration?
@MichaelHardy: When I first studied calculus in university I found it incredibly confusing that people just talked about $\mathrm{d}x$ as if it was some kind of object or variable you can use in normal calculations. Especially the physicists did that when using the total derivative. It really makes no sense until you define every single operation correctly and no introductory textbook that I know of does this. So, for freshmen, the grammar explanation may help to avoid frustration (it did for me).
Sep
7
answered Doubts about fundamental theorem of Homomorphism
Sep
6
awarded  Enthusiast
Sep
5
comment Splitting field and dimension of irreducible polynomials
Do you know about the multiplicativity formula $[M:K]=[M:L][L:K]$ where $M|L$ and $L|K$ are field extensions?