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1d
comment Finding a homography in $\hat {\Bbb {C}} $
there exists nonzero $a,b,c,d$ making all $4$ equations true if and only if there exists nonzero $a,b,c,d$ in the kernel of the matrix. And that kernel is nontrivial if and only if the determinant is zero.
1d
revised Finding a homography in $\hat {\Bbb {C}} $
added 627 characters in body
1d
answered Finding a homography in $\hat {\Bbb {C}} $
2d
comment $F[t]$ has undecidable positive existential theory in the language $\{+, \cdot , 0, 1, t\}$
to me none of this make any sense
Jul
28
comment Proposition: $\sqrt{x + \sqrt{x + \sqrt{x + …}}} = \frac{1 + \sqrt{1 + 4x}}{2}$.
this is not absurd in $2$-adics numbers
Jul
27
comment Determine the galois group of $x^5+sx^3+t$
Also, can't you do a base change over $\Bbb C$ to reduce it to a geometry problem ?
Jul
27
comment Is Every transcendental entire function $f(z) = C + \exp a + \exp b + \exp c $?
What's a transcendental function ?
Jul
26
comment I need help proving the base case for a mathematical induction proof
it's not $2n$ and $2n+1$ but $2^n$ and $2^{n+1}$
Jul
25
awarded  Revival
Jul
24
comment Global structure of the Gromov-Hausdorff space
what's $Z{}{}$ ?
Jul
24
answered Wizard against two dwarfs: guess the whole function
Jul
23
comment Every non-increasing sequence of polynomial towers stabilizes — Finitary proof
To me this sounds like wanting to prove that $\varepsilon_0$ is well-ordered, which is kinda hard.
Jul
23
comment Wizard against two dwarfs: guess the whole function
Assuming the Axiom of Choice, they can reduce the problem to this question math.stackexchange.com/questions/371184/predicting-real-numbers/… by both picking $S_1 = \Bbb R \setminus \Bbb N$ and discarding the info the wizard tells them.
Jul
22
comment Fibonacci $\equiv -1 \mod p^2$
alright, also it's just $(X-\phi^m)(X+\overline{\phi}^m)$ and that threw me off. Also, I think you have a few wrong signs in the following two lines, at least the $\pm$ should be in fron of $1$ and $3$ and not $\sqrt 5$, but it shouldn't break everything.
Jul
22
comment Fibonacci $\equiv -1 \mod p^2$
I don't get how you deduce that $\varphi^m$ has to be a root of $X^2 + \sqrt 5 X + (-1)^m$
Jul
19
revised Nature of the roots of quadratic equation
added 116 characters in body
Jul
19
answered Nature of the roots of quadratic equation
Jul
18
comment What function satisfies $F'(x) = F(2x)$?
the power series's radius of convergence is zero though.
Jul
16
comment primitive element $a$ of $\mathbb F_{p^n}/\mathbb F_p$ such that $a^n\in\mathbb F_p$
what's a primitive element ?
Jul
15
comment A question about polynomial in two variables
I don't understand wether $f_1(2)$ is $f(1,2)$ or $f(2,1)$.