Timeline for On the fixed point of automorphism of $\mathbb F_3[[T]]$

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Dec 16, 2013 at 22:35	comment	added	Michael Zieve		Jonathan, yes that's correct, but that isn't the potential generalization they studied (and showed didn't exist) in the paper with Bleher and Poonen.
Dec 16, 2013 at 17:48	comment	added	Lubin		Mike, I thought that the Chinburg-Symonds example ($p=r=2$) was just a really nice formal expansion of the $i$-automorphism of a supersingular elliptic curve over $\mathbb F_2$ whose endomorphism ring over that field is $\mathbb Z[i]$.
Dec 16, 2013 at 8:06	comment	added	Michael Zieve		@Yves: nice! That's much nicer than my argument, so I edited it into my answer.
Dec 16, 2013 at 8:05	history	edited	Michael Zieve	CC BY-SA 3.0	deleted 99 characters in body
Dec 16, 2013 at 7:54	comment	added	YCor		Your argument for finite order can be simplified: the symmetric polynomial can just be chosen to be the product $X_1X_2\dots X_n$, since it is an element of valuation $n$, it is not a constant. In other words, if $\sigma$ has order $n$ then it fixes the nonconstant element $\prod_{i=0}^{n-1}\sigma^i(T)$.
Dec 16, 2013 at 6:43	history	edited	Michael Zieve	CC BY-SA 3.0	added 1187 characters in body
Dec 16, 2013 at 6:38	history	edited	Michael Zieve	CC BY-SA 3.0	added 1187 characters in body
Dec 16, 2013 at 5:32	history	answered	Michael Zieve	CC BY-SA 3.0