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I'm a student of mathematics in Germany.


1h
comment Is reduced homology a full functor on connected spaces?
@studiosus Thanks. I guess you could make that an answer here as well. Do you also have a counterexample for when $X = Y$?
1h
asked Is reduced homology a full functor on connected spaces?
12h
revised Inflating open sets up to homotopy through CW skeletons
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13h
revised Inflating open sets up to homotopy through CW skeletons
edited title
1d
revised Inflating open sets up to homotopy through CW skeletons
edited body
1d
asked Inflating open sets up to homotopy through CW skeletons
1d
awarded  Electorate
2d
comment Is there a notation for being “a finite subset of”?
I like your second variant. I often write something like $A \underset{\smash{\scriptsize \text{finite}}}{⊂} B$ myself (which looks better when handwritten). I think this will be understood by everyone immediately, so I wouldn’t worry about using it.
2d
comment How is induction justified in intuitionistic logic?
Not from Bonn, if you’re hinting at that! ;) Thanks for the elaborate answer.
2d
accepted How is induction justified in intuitionistic logic?
2d
revised How is induction justified in intuitionistic logic?
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2d
asked How is induction justified in intuitionistic logic?
Jan
25
comment Number of units of $\mathbb{Z}/11\mathbb{Z}$ and $\mathbb{Z}/12\mathbb{Z}$
$ℤ/11ℤ$ is a ring with a multiplicative identity $[1]_{11ℤ}$ and $11$ is the number of all elements in $ℤ/11ℤ$. The units of $ℤ/11ℤ$ are the elements in it which are invertible with respect to multiplication. For example, $[0]_{11ℤ}$ is not multiplicatively invertible.
Jan
24
comment Expected number of days of watching movie
You choose a subset of movies, yet only the probability of choosing a movie is mentioned. Is the subset of fixed size (for all days)?
Jan
24
comment Linear subspace of K[X]?
@Sai Well, then use the time to pep it up a bit. Interpret $I_v$ as the kernel of some suitable linear map.
Jan
24
comment How can we think and/or write rigorously about integration by substitution?
Not that I ever really understood this, but have you had a look at differential forms? (You can interpret $t$ as the identity map $t\colon ℝ → ℝ$ and $\sin t$ as $\sin ∘ t$. If you do that and use differential forms, I believe writing “Let $u = \sin t$, then $du = \cos t dt$” actually makes sense.)
Jan
23
comment What does rigoruous but non-technical mean?
I’d say: A rigorous book states all claims clearly and gives careful proofs considering all important points. A non-rigorous book might only explain ideas, omit details in proof or use arguments appealing to imagination, common sense or faith. A technical book might use very specific language to state and prove its theorems involving strange or very local definitions, giving little hope of understanding a deeper meaning of them. A non-technical book makes rather short and clear statements and proofs, conceptual and (possibly) abstract in nature.
Jan
22
reviewed Reject What is the (mathematical) point of geometric constructions?
Jan
22
reviewed Approve Is there a maximum value between open (0,1) set?
Jan
22
revised $f(x) \in R[X]$ irreducible $\Rightarrow (f(x))$ ideal?
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