Matt
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 Feb 27 awarded Favorite Question Feb 11 awarded Good Question Oct 7 awarded Good Answer Sep 20 awarded Yearling Sep 30 awarded Explainer Sep 20 awarded Yearling Sep 6 awarded Nice Answer Jul 2 awarded Curious May 25 comment Frobenius action on $\overline{\mathbb Q_p}$ @JyrkiLahtonen The Frobenius is never an automorphism in characteristic 0, so that proof doesn't apply. The map still makes sense in many situations. The question only claims that it is an automorphism of $\mathbb{F}_p$. May 21 comment Étale cohomology and Picard group of curves Do you want $X$ to be defined over $\overline{\mathbb{Q}}$ or $\mathbb{Q}$? May 11 comment Is Calculus a requirement for Better Statistics? I'd strongly disagree with the "data science" person part. Most of a data scientists job is to build the models. You absolutely cannot build a good model without knowing the inner workings of the techniques. I don't know what pure statisticians do in the real world, but I would also imagine they build models too. Apr 28 revised An isogeny of elliptic curves induces a $\mathbb{Z}_l$-linear map incorporated a comment into the answer Apr 26 answered An isogeny of elliptic curves induces a $\mathbb{Z}_l$-linear map Apr 25 comment Find the maximal $p$-divisible subgroup of $(\mathbb{Q},+)$ and $(\mathbb{Q}^{\times},\cdot)$? It is possible that a group $G$ has no maximal subgroup, but there is a maximal subgroup satisfying an additional property. For example, suppose there was only one proper subgroup with that property. Apr 24 comment What is ${\rm cov}(e_i, \hat y_i)$ in simple linear regression? Cross-posted: stats.stackexchange.com/questions/94967/… Apr 23 comment Frobenius on projective variety is not an isomorphism? Notice that when you have a morphism explicitly given in coordinates you can compute the Jacobian to see what the induced map on tangent spaces is. In this case it is the zero map because of the characteristic! An isomorphism must induce an isomorphism on tangent spaces as well. In other words, the Frobenius morphism is singular everywhere. Apr 22 comment Why doesn't SAGE understand reduced expressions mod p in a finite field extension? Also, I think for GF(p) you are fine just assuming that it stores the representative classes as integers, but in general I would write GF(p^n, repr='int') to force the representatives to be integers. Apr 22 comment Prove that $r^n/n!$ converges where $n\ge r$ I think there is a typo. What does $n\geq r$ have to do with anything? Aren't you proving something where $n\to \infty$? Apr 20 comment What should one do if one works on a problem and submits a paper only to find that it is already in some book? Is it the exact same proof? I know of tons of published papers called things like "A New Proof of ... " Apr 19 comment Computing the genus in positive characteristic It seems likely that you won't be able to "rule out" wild ramification ... because depending on the degree $d$ there will be cases where you do have wild ramification. I remember doing this problem a few years ago and found it fun and enlightening. I'll play around with it later today to see if I remember how it goes.