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1d
comment What is the group structure on the ring of power series around a point that makes it “the completion of an elliptic curve” along that point?
I think you’re making it much too hard, and also hoping for something that (I think) doesn’t exist. More via private communication.
1d
awarded  Nice Answer
1d
comment $2$-adic sequence converging to $\sqrt{-7}$.
No, the series is not convergent when you plug in $-1$ for $t$; I didn’t say it was. But since the $n$-th degree (in $t$) term is divisible by $2^n$ after the substsitution, you definitely get a convergent series. It converges to $\sqrt{-7}$ because when you take the series in $t$ and square it, you get $1+4t$. This process is consistent with the procedure of substituting something small for $t$
2d
answered $2$-adic sequence converging to $\sqrt{-7}$.
2d
answered How to prove that the line perpendicular to the radius is the tangent in the calculus sense?
Jul
29
comment 8 cubes ($2$x$2$x$2$) crossed by a straight line
@HenningMakholm, thanks, that looks right.
Jul
29
comment 8 cubes ($2$x$2$x$2$) crossed by a straight line
Well, @JamesZen, think of the three mid planes. One horizontal, one east-west, one north-south. Now your line may cross each of these mid planes, or may not. Each time it crosses a plane, it goes from one cube to another. And you see that this is the only way a line can go from one cube to another. At most three passages from one cube to another, hence at most four cubes are visited.
Jul
28
comment 8 cubes ($2$x$2$x$2$) crossed by a straight line
Probably, @Michael. The complete proof needs a verifying example.
Jul
28
answered 8 cubes ($2$x$2$x$2$) crossed by a straight line
Jul
28
comment Choice of Primitive Element in ''Primitive Element Theorem''
Oh, well, then look closely at the suggestion of @GitGud; or else just take a normal extension of $\Bbb Q$ of degree three. If it were generated by a cube root, then the cube roots of unity would be there too, no good because the cube roots of unity are quadratic over $\Bbb Q$.
Jul
28
comment Why Composition and Dihedral Group have reverse order of operation?
If my memory serves me, back when I was in grad school (an earlier geological era), there were a couple of algebra text books that used the notation $(x)f$ — “take $x$ and $f$ it”.
Jul
27
comment Unicity in $p$-adic Weierstrass Preparation Theorem: dividing both sides of an equation of formal power series
I think I’m with you on this issue. But then, I would never have proved WPrep by what seems to be Koblitz’s method.
Jul
26
comment Unicity in $p$-adic Weierstrass Preparation Theorem: dividing both sides of an equation of formal power series
It’s not convenient for me to get hold of Koblitz’s book. Could you say what Lemma 8 says?
Jul
26
comment The algebraic closure of $\mathbb{Q}_p$
Why don’t you just find an irreducible polynomial of every degree? Much simpler.
Jul
25
awarded  Explainer
Jul
24
comment Third point of intersection is also a point of inflection?
Certainly, @GeorgesElencwajg. But nothing works till the neutral point is fixed at an inflexion point.
Jul
23
comment Choice of Primitive Element in ''Primitive Element Theorem''
You’re asking whether every extension is radical.
Jul
23
comment if $w1$, $w2$, …, $wn$ are the nth roots of (-1), then find their wronskian
OP might mean the Van Der Monde determinant.
Jul
23
comment Neukirch's motivation for $p$-adic numbers
Well, one can argue forever on this, but I maintain that the only “natural” coefficients for $\Bbb Z_p$ are the Teichmüller representatives, which (except for $2$ and $3$) aren’t in $\Bbb Z$.
Jul
23
answered Third point of intersection is also a point of inflection?