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1h
comment Why lower case “a” for “abelian group” and upper case “C” for “Cauchy sequence”?
Remember that in English we have a category that doesn’t exist in French: the proper adjective. The question then is only one about English; there’s no doubt that a pedant would object to “abelian group”. My upbringing was that the groups take his name uncapitalized, but Abelian varieties take the capital. Go figure.
11h
answered Fermats little theorem for p-adic integers
11h
comment Roadmap to $p$-adic numbers: where a self-learner should look for references
You might look into “Local Fields and their Extensions” by Fesenko and Vostokov.
11h
comment Fields of characteristic $p$ that are isomorphic as vector spaces, but not as fields
Whoops: your examples are OK: the first is a genus-zero ff with constant field $\Bbb F_2$, the second is also genus zero, but the constant field is $\Bbb F_4$.
11h
comment Fields of characteristic $p$ that are isomorphic as vector spaces, but not as fields
Zev, I think your two examples are both function fields of genus zero over $\Bbb F_2$. My examples would be $\Bbb F_2(T)$ itself and $\Bbb F_2(T)[Y]/(Y^2+Y+T^3)$. The latter is a ff of genus one, so definitely not isomorphic to the former.
11h
comment Explain why $e^{i\pi} = -1$ to an $8^{th}$ grader?
This is my preferred argument. However, I once attempted to charm a second-term Calculus class in a liberal arts college with it, and the response was to ask me whether it was good for anything. If I had had my wits about me and the forethought, I would have prepared myself by being able to quote the Millay sonnet, “Euclid alone has looked on Beauty bare.”
17h
answered Decomposing the ring of integers of a number field as a sum of prime plus field fixed by ramification group
18h
comment Galois group of $ \mathbb{Q}(\varepsilon_5) / \mathbb{Q} $
The way to show that $(x^p-1)/(x-1)=\varphi(x)$ is irreducible is to expand $\varphi(x+1)$. Best to do it before accomplishing the division! (It Eisensteins.)
21h
comment Finding the fixed Field of $\sigma \in Aut(\mathbb{R}(t)/\mathbb{R})$
Oh sorry, blame an old man’s poor vision. I thought those were $1$’s up top, not $t$’s to the power $1$. Then to @Spooky I would precisely echo anon’s comment. (Again, sorry!)
1d
comment Can a field extension still have “non-separability” above its maximal purely inseparable subextension?
Isn’t $K=F$ in this example?
1d
comment Finding the fixed Field of $\sigma \in Aut(\mathbb{R}(t)/\mathbb{R})$
@Spooky, that rational function is not the quotient of two odds, nor of two evens, so is not in $\Bbb R(t^2)$.
1d
comment Finding the fixed Field of $\sigma \in Aut(\mathbb{R}(t)/\mathbb{R})$
I just made the correction for @Spooky
1d
revised Finding the fixed Field of $\sigma \in Aut(\mathbb{R}(t)/\mathbb{R})$
corrected a typo
2d
comment Subgroups of automorphisms of Finite fields
You seem to be counting the automorphisms of your big field as finite group. But you need to look at field automorphisms, which are far fewer in number.
2d
answered Is the degree of an infinite algebraic extensions always countable?
May
23
comment Hensel's lemma & $p$-adic polynomial roots
For $p=5$, Eisenstein applies, since all coeffs are divisible by $5$ and the constant is not divisible by $25$. So irreducible, no roots in $\Bbb Z_5$.
May
23
answered Hensel's lemma & $p$-adic polynomial roots
May
23
comment How to find minimal polynomial of primitive element (field theory)
The way to show that $X^6+X^3+1$ is irreducible over $\Bbb F_2$ is to observe first that any root of this polynomial is a primitive ninth root of unity; then to observe that you need to go all the way to $\Bbb F_{64}$ before you find any elements of multiplicative period $9$. Since the big field is of degree six over the little, your polynomial is irreducible.
May
22
comment How to find minimal polynomial of primitive element (field theory)
Precisely what do you mean by “primitive element”? Do you mean a generator of the multiplicative group, which is the interpretation of @GerryMyerson, or do you mean an element $\alpha$ such that $k=\Bbb F_2(\alpha)$?
May
21
comment Constructing a Fractional Linear Map
Yeah, I think that this definitely is not the right idea. Any such $\varphi$ will be a rotation of $120^\circ$ about some point.