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Oct
23
suggested approved edit on Must a solution defined for $(t_0,+\infty)$ with bounded limit in $+\infty$ tend to a constant solution?
Oct
23
comment Must a solution defined for $(t_0,+\infty)$ with bounded limit in $+\infty$ tend to a constant solution?
@JuliánAguirre Would you please elaborate? I'm very interested in the autonomous case.
Oct
23
asked Must a solution defined for $(t_0,+\infty)$ with bounded limit in $+\infty$ tend to a constant solution?
Oct
22
revised Stability of autonomous linear systems of ODEs
added 481 characters in body
Oct
21
asked Stability of autonomous linear systems of ODEs
Oct
18
awarded  Yearling
Oct
12
comment Particular case of Nakayama's lemma
@Jack Ah, I see. Using elements as I was doing, it's $m=an_1\in M \Rightarrow m=a^2n_2\in M \Rightarrow \dots \Rightarrow m=a^kn_k=0$. Thank you.
Oct
12
asked Particular case of Nakayama's lemma
Oct
10
comment Isn't it cheating to consider an $ \mathbb{R}^3 $ vector as a “pure quaternion”?
@Mariano: what is MU?
Oct
1
comment Square roots of $-1$ in quaternion ring
Ouch, I found my mistake. I must remember that the binomial theorem only works in commutative rings. Thank you!
Oct
1
asked Square roots of $-1$ in quaternion ring
Sep
28
comment What makes simple groups so special?
Related: math.stackexchange.com/questions/25315/…
Sep
28
answered Why is any compact metric space the union of a countable set a subset which is a perfect space under the induced topology?
Sep
27
comment Why is any compact metric space the union of a countable set a subset which is a perfect space under the induced topology?
See en.wikipedia.org/wiki/Cantor%E2%80%93Bendixson_theorem
Sep
19
comment Is there a more efficient method of trig mastery than rote memorization?
@GiuseppeNegro: I think you should expand your comment into an full-fledged answer, expanding on your claim. I would certainly vote you up ;)
Sep
16
comment free $R$-algebras: when does $R\langle X\rangle\cong\!R\langle Y\rangle$ $\Rightarrow$ $|X|\!=\!|Y|$ hold?
+1 for a well-posed, motivated question.
Sep
11
comment Motivation for Eisenstein Criterion
@Qiaochu: In Gallian's book, he states the "Mod p irreducibility test" with an additional hypothesis, which is that the reduced polynomial mod $p$ must have the same degree as the original polynomial in $\mathbb{Z}$ for the implication "irreducible over $\mathbb{Z}_p\Rightarrow$ irreducible over $\mathbb{Q}$" to work (and it seems an important point to the proof). Why don't you require it? Can it be proven without that hypothesis?
Sep
11
comment Showing $\sup \{ \sin n \mid n\in \mathbb N \} =1$
Related: math.stackexchange.com/questions/4764/…
Sep
8
comment Methods to see if a polynomial is irreducible
...if $a$ is a unit.
Sep
7
comment What's the index of a subfield?
As a comment, I'd like to point out that using the same notation for different notions (degree of a field extension and index of a subgroup) is useful, the Galois correspondence theorem being its prime evidence.