106,359 reputation
696194
bio website von-eitzen.de/math/tntrep.xml
location Bonn, Germany
age 48
visits member for 1 year, 11 months
seen 34 mins ago

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


31m
comment Question about the proof of this lemma: If $\alpha$, $\beta$ are ordinals, then either $\alpha \subset \beta$ or $\beta \subset \alpha.$
We can work with ordinals even in set theories without the axiom of regularity. Hence using the definition of ordinals instead of regularity is fine (and in my eyes to be preferred)
16h
answered Why are those objects initial or final obejcts?
16h
comment Why are those objects initial or final obejcts?
So for 1) (where objects are sets and morphisms are just maps), can you show that for all sets $Y$, there exists exactly one map $\emptyset\to Y$ and exactly one map $Y\to\{*\}$?
16h
comment RSA encryption. Breaking 2048 keys with index
Well, it seem that RSA themselves didn't know (or were financially persuaded not to know) that fact for a while ...
19h
answered A property regarding intervals
19h
revised Unit circle is divided into $n$ equal pieces, what is the least value of the perimeters of the $n$ parts?
added 205 characters in body
19h
revised Unit circle is divided into $n$ equal pieces, what is the least value of the perimeters of the $n$ parts?
added 205 characters in body
23h
answered Unit circle is divided into $n$ equal pieces, what is the least value of the perimeters of the $n$ parts?
1d
comment Tangent line at $x_1$ to polynomial curve $p(x)$ of degree at least $2$ implies $x_1$ is a double root of $p(x) - p^{'}(x_1)(x-x_1)$?
@user111854 if $h(x)=(x-x_0)^kh_1(x)$ with some polynomial $h_1$, then $h'(x)=k(x-x_0)^{k-1}h_1(x)+(x-x_0)^kh_1'(x)=(x-x_0)^{k-1}h_2(x)$ with $h_2(x):=kh_1(x)+(x-x_0)h_1'(x)$, i.e. each higher derivative has one factor $(x-x_0)$ less.
1d
answered Tangent line at $x_1$ to polynomial curve $p(x)$ of degree at least $2$ implies $x_1$ is a double root of $p(x) - p^{'}(x_1)(x-x_1)$?
Jul
25
comment RSA encryption. Breaking 2048 keys with index
In other words, the key to breaking the randomly generated keys is to convince people to use your specialized random number generator :)
Jul
23
comment Paradoxical Game Show Problem
As soon as you impose a probability distribution on the money amounts, the paradox gets resolved (because when seeing an unusually high amount in your chosen box, the probability that yours is the smaller amount decreases)
Jul
23
revised finding a group that satisfy: $x,y\in A_n\Rightarrow x\in y \vee y\in x \vee y=x$
edited tags
Jul
23
comment finding a group that satisfy: $x,y\in A_n\Rightarrow x\in y \vee y\in x \vee y=x$
What about the set $n$ itself?
Jul
23
answered Equivalence Graphs
Jul
23
comment My proof of the recursion principle (without the axiom of replacement)
I'm not very happy with "maximum element of domain". Why not use replacement to take the domain of $f$ itself? (This may require some special cases near $0$) Or do you already have $n^-$ on $\mathbb N\setminus\{0\}$ readily available?
Jul
23
comment Calculate distance between two objects based on their visible height for a specific focal length
A focal length of 35mm means that a point at infinity is mapped to a point 35mm behind the lens. However if your 15cm object is mapped to an image of 12cm, i.e. almost its original size, we are talking about the lens moved considerably away from the image plane (namely approximately into the middle between image plane and object; we'd have exactly the middle if the image size were equal to the object size). At any rate, without additional information, only the relative distances of the objects from the lens can be inferred from the quotient of their sizes.
Jul
23
comment Prove that intersection of connected spaces is connceted.
Let $A$ be the unit circle and $B$ the $x$-axis within the two-dimensional plane. Which of $A,B,A\cap B$ are conncted?
Jul
23
comment Why does this graph only the positive side
Hint: Do you think that $\sqrt[4]{x^2}=x^{2/4}=x^{1/2}=\sqrt x$ for all real numbers $x$?
Jul
23
answered Question concerning how a map extends to a homomorphism.