Ted Chinburg (University of Pennsylvania)
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| It's an old problem to find "explicit" formulas for an automorphism of order p^2 of k[[t]] when k is a field of positive characteristic p. I will talk about some of the history of this problem and then a particular formula for an automorphism of order 4 when p = 2. This formula turns out to be characterized as the unique formula of its kind arising from an "extra automorphism" of a Katz-Gabber cover of the projective line. This is joint work with Frauke Bleher and Peter Symonds. |