Reputation
5,219
Next privilege 10,000 Rep.
Access moderator tools
Badges
2 14 36
Newest
 Nice Answer
Impact
~74k people reached

Aug
17
comment a conjectured new generating function of narayana's sequence
Your recurrence relation isn't quite right
Aug
16
comment Why is any number divided by 0 is infinite?
my point is that there's a standard definition of $f(x) \to \infty$ as $x \to 0$, but your example doesn't fit it. You could say that $1/x \to \infty$ as $x \to 0$ from above, and that would be right :)
Aug
16
comment Why is any number divided by 0 is infinite?
no, still wrong. That limit doesn't exist (consider negative $x$)
Aug
16
comment Why is any number divided by 0 is infinite?
it is not accurate to say that "$1/0 \to \infty$" Tending to infinity or not is a property of a sequence, not of a symbolic expression like $1/0$.
Aug
14
comment What to do when confronted with hard problems?
Polya says when you're stuck, ask yourself: "Can I solve an easier version of this problem?"
Aug
5
revised Flock of Pigeons - Thousand and One Nights
edited tags
Jul
30
comment Squaring is linear in Galois Field $2$
It is not true that squaring is linear in all fields on characteristic two -- only that it is additive.
Jul
30
comment Making sense of the term $H^1(N,A)^{G/N}$ in the inflation-restriction exact sequence.
See Benson - Representations and Cohomology II section 3.5 for a description of how this action is defined. Briefly, you take a $kG$-projective resolution of $k$ which is a $kN$-projective resolution by restriction, so can be used to calculate $H^1(N,A|_N)$. Then the space of $N$-homs from this resolution to $A$ is a $G$-module ($(g\cdot f)(q)=gf(g^{-1}q)$), but $N$ acts trivially, hence it becomes a $G/N$-module. This induces an action on the Ext-groups.
Jul
29
comment A problem about isomorphism in module theory
Standard counterexample for questions like this: $R=\mathbb{Z}$, $B= \mathbb{Z} \oplus \mathbb{Z} \oplus \cdots$, $\ker g = \mathbb{Z} \oplus \mathbb{Z} \oplus 0 \oplus 0 \oplus \cdots$, $\operatorname{im} f = \mathbb{Z} \oplus 0 \oplus 0 \oplus \cdots$
Jul
29
comment In general, how do you construct a nontrivial representation of a group?
Every group has a regular representation, which is nontrivial so long as the group is nontrivial.
Jul
28
comment Hint to find the order of the group of $2\times 2$ matrices under multiplication
math.stackexchange.com/questions/1200622/… math.stackexchange.com/questions/901654/… math.stackexchange.com/questions/296047/… ...
Jul
28
revised Is “Categories and Sheaves” a good followup to Aluffi's “Algebra: Chapter 0”?
added 20 characters in body
Jul
21
awarded  Nice Answer
Jul
14
answered Is it possible to put an equilateral triangle onto a square grid so that all the vertices are in corners?
Jul
11
comment What are “instantaneous” rates of change, really?
@Henning NSA doesn't require you to shift back and forth between reals and hyperreals, for example there are no hyperreals in the IST approach.
Jul
10
reviewed Approve Evaluating an indefinite integral with a square root in the denominator
Jul
8
comment Recommendation for books on topology (light reads)
A topological picturebook by George Francis?
Jul
8
comment arithmetic with quantum integers
The relationship is that the first $[n]_q$ is equal to $q^{-n+2}\{ n\}_{q^2}$ where the curly brackets denote the second kind of $q$-integer. This means you can derive multiplication formulas for the first kind from ones for the second.
Jul
8
comment Prove or disprove $A_5$ has a subgroup that isomorphic to $\mathbb{Z}_6$
math.stackexchange.com/questions/1246662/…
Jul
8
comment Noncyclic Abelian Group of order 51
There is no need for the Sylow theorems here! The result you mention is Cauchy's theorem, much simpler than Sylow's theorems.