92,385 reputation
581169
bio website von-eitzen.de/math/tntrep.xml
location Bonn, Germany
age 48
visits member for 1 year, 7 months
seen 6 hours ago

I did study math and had a knack for it, but I am sooo out of that business now ...


2d
answered Largest determinant of a real $3\times 3$-matrix
2d
comment Implication or Bidirectional in “x is a Prime”
@MauroALLEGRANZA Come to think of it, to be valid in a more general context (say, beyond predicate calculus) instead of an axiom one may need something like "can be relaced in any context (obeying possible type/variable restrictions)", I assume
2d
comment What's the best strategy to count the eggs in the jar?
If the jar were near my desk, the number would at least be (almost strictly) decreasing :)
2d
comment Axiomatizing topology through continuous maps
The maps should be closed under composition (so we have in fact a category) and the maps from an arbitrary space to $Z$ should be closed under finite min and arbitrary max and include the constant maps?
2d
comment Why f' is zero a.e. where f zero?
Maybe: There exists $g$ such that $g(x)=f(x)$ a.e. and $g'(x)=0$ on $\{\,x\mid g(x)=0\,\}$?
2d
comment What's the best strategy to count the eggs in the jar?
a) Open the jar and count - b) weigh (requires an empty jar and identical egg to compare) - c) find out what others guess and make a guess in the largest gap in the reasonable range (if you don't know what others guess, assume they guess round numbers)
2d
awarded  Nice Answer
2d
answered Finding probability of a random point
2d
answered Prove that if graph $G$ is a 3-connected planar graph then its dual must be simple.
2d
comment A question about limsup and limif
What about $a_n=\frac{(-1))^n}{n}$, $A=-0.01$, $B=0.01$? We have $A<\liminf a_n=0=\limsup a_n<B$ and yet $A<a_n<B$ does not hold for $n<100$??
2d
answered Show that two points from four are at a distance $\leq \sqrt{3}$ in an equilateral triangle.
2d
answered Implication or Bidirectional in “x is a Prime”
2d
comment What would be an example such that $aH=bH$ but $Ha \neq Hb$?
@Amr A non-normal subgroup in an abelian group would be fine as well, if one could find such :)
2d
answered Is this already an equation/law that has been found?
2d
comment Cyclic and abelian group
Is here power = order or power = exponent?
2d
comment Suppose that $\sum a_i$ converges and that $a_i\geq0$ for all 𝑖.
Where do you get stuck? Use the definition and show that the partial sums are a Cauchy sequence.
2d
comment Proving a relation is a total order relation
Are you insisting on the "either - or" here? I.e. do you consider "$\le$" or do you consider "$<$" an order relation? Or do you complain because the proof in this form would also erroneously "show" that "divides" is a total order on $\{-2^n,-2^{n-1},\ldots,-4,-2-1,1,2,4,\ldots,2^n\}$?
2d
comment Prove $M$ is a Maximal Ideal in $\Bbb Z\times \Bbb Z$
$M$ is the kernel of $\mathbb Z\times\mathbb Z\to\mathbb Z/p\mathbb Z$, $(x,y)\mapsto x+p\mathbb Z$
2d
comment Conditions on $f:[a,b]\to \mathbb{R}$ to ensure a finite number of crossings
It i sof course sufficient to study the case that $f$ is differentiable on $(a,b)$. And one sifficient condition is of course that $(f')^{-1}(\{0\})$ is finite.
Apr
15
comment How can I learn Real Analysis in 10 days?
Well, it is also possible to learn playing the piano in 88 days, and it is sufficient to learn one key per day.