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Results for hensel's lemma
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52 votes

What would a "moral" proof of the Weil Conjectures require?

(For example, in the case of primitive roots, there is basic field theory combined with Hensel's lemma/Newton approximation; this style of argument extends, in some form, to the very general setting of …
Emerton's user avatar
  • 57.6k
50 votes
6 answers
6k views

Intuition for the last step in Serre's proof of the three-squares theorem

To show it is sufficient, a lemma of Davenport and Cassels, using Hasse-Minkowski, shows that $a$ is the sum of three rational squares. … Complete the analogy: Hensel's lemma is to Newton's method as this technique is to _____________________. …
Qiaochu Yuan's user avatar
48 votes

Example of connected-etale sequence for group schemes over a Henselian field?

Lemma and the primitive element theorem. … By using Hensel's Lemma in finite local $R$-algebras, to give a map from a finite \'etale $R$-algebra $A$ to a finite $R$-algebra $B$ is the same as to give a map $A_0 \rightarrow B_0$ between their special …
BCnrd's user avatar
  • 7,108
37 votes

Over which fields are symmetric matrices diagonalizable ?

If its eigenvalues mod $x$ are all distinct, we are done, because we can find roots of its characteristic polynomial in $\mathbb R[[x]]$ by Hensel's lemma. … Lemma: Let $M$ be a symmetric matrix over $\mathbb R[[x]]$ such that some eigenvalues are distinct mod $x$. …
Will Sawin's user avatar
  • 148k
32 votes
1 answer
1k views

Are there any integers which can't be written as a sum of two fourth powers minus a cube?

.$ Using the Chinese Remainder Theorem and Hensel's Lemma one can quickly reduce this claim to the case that $n=p$ is a prime. …
zeb's user avatar
  • 8,688
28 votes
Accepted

Which p-adic numbers are also algebraic?

The idea is that this field is not complete but is Henselian -- it satisfies the conclusion of Hensel's Lemma. …
Pete L. Clark's user avatar
27 votes
Accepted

p^2 dividing n^8-n^4+1

By Hensel's Lemma, the square of a prime $p\geq 5$ divides $\Phi_{24}(n)$ for some $n$ if and only if $p$ divides $\Phi_{24}(m)$ for some $m$. …
GH from MO's user avatar
  • 105k
26 votes

Are there results in "Digit Theory"?

Appearances can sometimes be deceiving: automorphic numbers may at first look totally recreational, but they are connected with the Chinese remainder theorem, Hensel's lemma, and the contraction mapping …
KConrad's user avatar
  • 50.6k
26 votes

Examples of famous 'workhorse' theorems

but not too difficult (Nakayama's lemma, Hensel's lemma, Sperner's lemma). … However, there do exist "high-powered" examples such as the fundamental lemma or the Szemerédi regularity lemma. …
26 votes
3 answers
6k views

An unfamiliar (to me) form of Hensel's Lemma

He says that this result is today called Hensel's Lemma and that Hensel's standard proof applies. … It was my initial thought that the Hensel-Kurschak Lemma would follow easily from one of the more standard forms of Hensel's Lemma. …
Pete L. Clark's user avatar
26 votes
Accepted

Diophantine equation with no integer solutions, but with solutions modulo every integer

example, the Diophantine equation $(x^2 - 2)(x^2 - 3)(x^2 - 6) = 0$ has this property: for any prime $p$, at least one of $2, 3, 6$ must be a quadratic residue, so there is a solution $\bmod p$, and by Hensel'slemma (which has to be applied slightly differently when $p = 2$) there is a solution $\bmod p^n$ for any $n$. …
Qiaochu Yuan's user avatar
25 votes

Why is the motivic category defined over the site of smooth schemes only?

lemma"); this is what makes localization work for sheaves on the small Nisnevich or étale sites. … The key input here is a geometric presentation lemma of Gabber, a statement of which can be found as Lemma 15 in the introduction to Morel's book (http://www.mathematik.uni-muenchen.de/~morel/Prepublications …
Marc Hoyois's user avatar
  • 8,972
25 votes
Accepted

Irreducible polynomial over number field with roots in every completion?

Hensel's lemma comes with hypotheses. …
user avatar
24 votes
Accepted

Cryptomorphisms

In my class today, I presented the "Omnibus Hensel's Lemma". Part a) was: the following five conditions on a valued field are all equivalent. … For instance, the origin of the question I cited above was the fact that in Tuesday's class I stpdly chose the wrong form of Hensel's Lemma to use to try to deduce yet another version of Hensel's Lemma
24 votes

Field complete with respect to inequivalent absolute values

Of course having an isomorphism in this case depends on Zorn's lemma, so field isomorphisms $\mathbf C_p \to \mathbf C$ are totally nonconstructive. … Thanks to Hensel's lemma and finiteness of the residue field of $(K,|\cdot|)$, we can describe the group $\mathcal O_K^\times$ purely algebraically: $$ \mathcal O_K^\times = \{x \in K^\times : x {\sf \ …
KConrad's user avatar
  • 50.6k

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