On the deformations of cyclic Galoi coverings of algebraic curves

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Our aim of this research is to construct a lifting of a couple (C,sigma) of a complete non-singular curve C over a field of characteristic p (>O), and its automorphism sigma of order p^n (n<greater than or equal>1). For the case of n = 1, we have obtained an affirmative result by using Lang's class field theory. In the argument, one of the important ideas if to construct a deformation of the Artin-Schreier theory to the Kummer theory, i.e., to construct a deformation of an additive group to a multiplicative group. Therefore when we try to solve the problem for n<greater than or equal>2, first of all, we must construct the deformations of the Witt group W_n to a torus (G_m)^n. We decided Completely such deformations for n=2 in 1988 and 1989. In 1990, we discovered a vanishing theorem for extensions of additive groups by a torus over an Artin local ring, and usinit we treated the extensions of group schemes over a Artin local ring. Moreover, by using the vanishing theorem, we succeeded in constructing the deformations of the Artin-Schreier-Witt exact sequence to an exact sequence of Kummer type. In future, we must construct a unified theory of the Artin-Schreier-Witt and the Kummer theories, and apply it to our original problem.