110,373 reputation
6101205
bio website von-eitzen.de/math/tntrep.xml
location Bonn, Germany
age 48
visits member for 2 years
seen 10 mins ago

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


Aug
31
answered Variation of Monty Hall problem
Aug
31
comment Folding sheets of paper
There are many lengths. What kind of description do you expect?
Aug
31
comment How I can imply that the supremum is in a set S?
Yes, that is one way to proceed.
Aug
31
comment How to calculate the cardinality of the intersection of three sets?
Yes, starting only from the original info, we can only input $n(A\cup B\cup C)\le 151$ into the i/e principle, which gives $n(A\cap B\cap C)\le 30$.
Aug
31
revised How to calculate the cardinality of the intersection of three sets?
added 99 characters in body
Aug
31
answered How to calculate the cardinality of the intersection of three sets?
Aug
31
comment Prove tautology without truth table
... and maybe associativity (used here implicitly by not using parentheses) needs to be mentioned explicitly.
Aug
31
comment Why induction cannot be used for infinite sets?
Not to mention that the more general statement $\left(\bigcup_{i\in I} A_i\right)^c = \bigcap_{i\in I} A_i^c$ holds - with an arbitrary index set $I$.
Aug
28
answered The probability of $n$ being a square, given the units-digit in its decimal representation
Aug
28
comment how to fairly select a leader
Why not allow people the freedom to vote about unkown candidates? Such as: Of the interviews with $a,b,c$, the last two turned out so awful, it is safe to assume that $d$ is better than $b,c$, so my priority is $adbc$ (or perhaps mixed with $dabc$).
Aug
28
comment The category with binary relations as objects
If the ordinary composition of relation turns Rel into a category (which it does), then the construction works ... Even if you want functions for horizontal and relations for vertical arrows, this doesn't really matter as the composition for functions is the composition for relations
Aug
27
comment topology defined on the set $\mathbb{R}^\mathbb{R}$?
The way you write it, the product topology might come to mind (though it ignores the topology on the exponent)
Aug
27
comment Polynomial modulus in Quotient Ring
If (a representative) $g$ is coprime to $x^m+1$, then $pg+q(x^m+1)=:d\in\mathbb Z$ for some polynomials $p,q\in\mathbb Z[x]$; in that case is $\tilde a$ can be chosen to be an constant polynomial $<d$. If $g$ divides $x^m+1$, then all we can do is reduce $a$ to degree $<m$. In the general case, I guess that combinig these results via the Chinese rRemainder Theorem gives what you want?
Aug
26
comment Proving surjectivity of a strictly monotone function
But $f$ is not necessarily bounded. However, we know that $g'(x)\ge 1-\frac aM$ is bounded away from $0$ ...
Aug
26
comment Countable Set & Formal Grammar
I suggest that 1 and 4 are true.
Aug
26
comment Defining a group from edge set of graph
Of course this attempt todefine a group structure works only if any two edges share a vertex ...
Aug
26
comment Find isomorphism between $\mathbb{Q}[T]/(T^2+3)$ and $\mathbb{Q}[T]/(T^2+T+1)$
@jjjx Of course my method has problems with polynomials in higher degree ...
Aug
26
answered Find isomorphism between $\mathbb{Q}[T]/(T^2+3)$ and $\mathbb{Q}[T]/(T^2+T+1)$
Aug
26
reviewed Leave Open Convergence of averaged sine function
Aug
26
reviewed Close Why is $0/0$ not $\Bbb R$?