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asked Proving a Function Continuous with Non-Standard Analysis
Feb
4
comment Finite Groups With Exactly Two Automorphisms
Here: math.stackexchange.com/questions/93782/…
Jan
26
comment Why can we prove things via the contrapositive, contradiction, etc.?
There are logic systems, like intuitionistic logic, that don't allow reductio and contrapositive.
Jan
14
awarded  Nice Question
Jan
12
awarded  Famous Question
Dec
31
comment Triple integral of $zx \sin(xy)$
Integrate with respect to $y$ with a substitution $u=xy$.
Dec
31
comment Why are there $12$ automorphisms of $\Bbb Z\oplus \Bbb Z_{3}$?
$2$ also generates $\mathbb{Z}_3$.
Dec
28
comment Function Riemann integrable that are not Lebesgue integrable.
Was the question "Prove or disprove"?
Dec
26
comment Mobius transformation and Group action
Im(g(i)) is always positive.
Dec
26
revised Mobius transformation and Group action
added 55 characters in body
Dec
26
comment Mobius transformation and Group action
What did you get for the orbits?
Dec
18
comment Is $ℝ^2$ a subspace of $ℝ^3$?
The subspace $\{ (x,y,0) \, | \, x,y\in \mathbb{R}\}$ is isomorphic to $\mathbb{R}^2$.
Dec
16
comment The intersection of any set with the empty set is empty
Seems fine to me.
Dec
14
answered Cyclic group given a group action
Dec
10
comment If $B$ is a square matrix such that $B^3= B$ then what can we say about the eigenvalues of $B$?
You forgot about $-1$.
Dec
7
comment Proof using matrices, when does $XA=XB$ imply $A=B$?
If you want it true for all $X$, then it must be true when $X$ is the identity matrix.
Nov
30
answered Show that $(H, \circ)$ is a subgroup of the group $G$
Nov
24
comment Limit Definition when Right-Hand Limit has Nonempty Domain but Left-Hand Limit has Empty Domain
You could say the left hand limit exists because for all sequences $x_1,x_2,\ldots$ of points such that $x_i<0$ and $x_i$ is in the domain, you have $f(x_i) \to 0$. It just happens that no such points exist.
Nov
19
comment Prove that $f(x)=x^2$ is not well defined on $\Bbb Z_{11}\to\Bbb Z_{22}$
Do you mean not well-defined, or not injective?
Nov
16
comment Is there a group with countably many subgroups, but is not countable in ZF?
Sorry about that. My brain added a "C" at the end of "ZF".