Cyclically valued rings and formal power series
Annales Mathématiques Blaise Pascal, Tome 14 (2007) no. 1, pp. 37-60.

Rings of formal power series k[[C]] with exponents in a cyclically ordered group C were defined in [2]. Now, there exists a “valuation” on k[[C]] : for every σ in k[[C]] and c in C, we let v(c,σ) be the first element of the support of σ which is greater than or equal to c. Structures with such a valuation can be called cyclically valued rings. Others examples of cyclically valued rings are obtained by “twisting” the multiplication in k[[C]]. We prove that a cyclically valued ring is a subring of a power series ring k[[C,θ]] with twisted multiplication if and only if there exist invertible monomials of every degree, and the support of every element is well-ordered. We also give a criterion for being isomorphic to a power series ring with twisted multiplication. Next, by the way of quotients of cyclic valuations, it follows that any power series ring k[[C,θ]] with twisted multiplication is isomorphic to a R [[C ,θ ]], where C is a subgroup of the cyclically ordered group of all roots of 1 in the field of complex numbers, and R k[[H,θ]], with H a totally ordered group. We define a valuation v(ϵ,·) which is closer to the usual valuations because, with the topology defined by v(a,·), a cyclically valued ring is a topological ring if and only if a=ϵ and the cyclically ordered group is indeed a totally ordered one.

Classification : 13F25,  13A18,  13A99,  06F15,  06F99
     author = {Leloup, G\'erard},
     title = {Cyclically valued rings and formal power series},
     journal = {Annales Math\'ematiques Blaise Pascal},
     pages = {37--60},
     publisher = {Annales math\'ematiques Blaise Pascal},
     volume = {14},
     number = {1},
     year = {2007},
     doi = {10.5802/ambp.226},
     mrnumber = {2298803},
     zbl = {1127.13019},
     language = {en},
     url = {}
Leloup, Gérard. Cyclically valued rings and formal power series. Annales Mathématiques Blaise Pascal, Tome 14 (2007) no. 1, pp. 37-60. doi : 10.5802/ambp.226.

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