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Jun
29
answered Proving that a real number is a non-negative integer.
Jun
29
comment Proving that a real number is a non-negative integer.
... and do $P,Q$ contain all or possibly just some of the primes dividing $n\pm k$?
Jun
29
revised Is there any algorithm or something to solve $\phi\left(x\right)=n$
added 1097 characters in body
Jun
29
answered Is there any algorithm or something to solve $\phi\left(x\right)=n$
Jun
29
awarded  Revival
Jun
28
answered What is the domain of the function
Jun
28
comment Is there something interesting about $373857714078$?
Does "blohillsbele" mean anything? At least that's the word you get by "turning the calulator"
Jun
28
comment Associativity of product law in $R^S$ ($R$ ring, $S$ a monoid with condition)
It should be $\gamma_w$, not $\gamma_t$ in the first sum
Jun
28
comment Probability of hitting numbers 1 - 12 on a single zero roulette wheel
Actually $\frac{12}{37}<\frac13$
Jun
28
answered What unit is the first derivative of a quadratic Bézier curve expressed in?
Jun
28
comment How do I prove this assertion?
Use the diagonal argument
Jun
28
answered If a set $E\subset \Bbb{R}^n$ is closed and open, then it is either $\Bbb{R}^n$ or $\emptyset$.
Jun
28
answered The Stabilizer of the coset for the action of G on $G/H$ by left multiplication.
Jun
28
comment If $f=u+iv:D\to \Bbb C$ is analytic on a domain D, is then the curves $u(x,y)=c_1$ and $v(x,y)=c_2$ intersect orthogonally?
Have a look at $f(z)=z^2$ and $c_1=c_2=0$. In what angles do your curves intersect and are they curves in the first place?
Jun
28
comment If $f=u+iv:D\to \Bbb C$ is analytic on a domain D, is then the curves $u(x,y)=c_1$ and $v(x,y)=c_2$ intersect orthogonally?
... if they intersect at all
Jun
28
answered How to determine if 2 line segments cross?
Jun
28
comment Does $\Bbb R-\Bbb Q$ have a well ordered subset of type $\omega\cdot\omega$
Actually, this is almost also a proof of the quoted theorem: Assume the ordinal $\alpha$ is countable and all $\beta<\alpha$ can be embedded into $\mathbb Q$. Then for each $\beta<\alpha$ pick a distinct one of the countably many intervals $(n.n+1)\cap\mathbb Q$, into which we can also embed $\beta$. The order type of the union is countable and contains each $\beta$, hence is $\ge\alpha$ and contains $\alpha$ as subset. - Finally if we find a copy $\alpha$ within $\mathbb Q$, we can translate it by $\sqrt 2$ and then find it within $\mathbb R-\mathbb Q$
Jun
28
answered Prove that the function $\xi\in R \mapsto {e^{i\cdot \xi\cdot λ}-1\over i\cdot \xi}-λ$ is $C^{\infty}$
Jun
28
comment Prove that the following function is $C^\infty$
Strictly speaking, $f$ is not even defined at $\xi=0$.
Jun
27
comment Is a nontrivial finite group of order $n$ always isomorphic to a subgroup of $GL_{n-1}(\mathbb{Z})$?
Or in another formulation: Consider the natural action of $G$ on $\bigoplus_{g\in G, g\ne e}(g-e)\mathbb Z$ where $h\cdot (g-e)=(hg-e)-(h-e)$