Basic de nitions and resultsDedekind-domains are de ned in several ways in the literature. We will give t h e one which is the most suitable for our purposes.De nition 1.1. Let R be an integral domain. We call R a Dedekind-domain, if for every ideal I of R we can nd prime ideals P 1 : : : P k unique up to ordering, such that I = P 1 : : : P k .For general properties of Dedekind-domains see 7], 15], 16], 26], 35] and 48]. the companion matrix of u. Remark 1.15. With the above notations we haveu n (d) = M(u) n u 0 (d) which will be used frequently in the paper.Remark 1.16. We mention that if we reduce a linear recurring sequence modulo some ideal in a Dedekind-domain, then we get a linear recurring sequence in the residue class system, which may have di erent properties than the original sequence (e.g. the minimal order of the reduced sequence may became smaller). By Remark 1.16 it has sense to introduce the following notations:De nition 1.17. Let s be a positive integer. With the notation of De nition 1.14 d P (u s) will denote the minimal order, % P (u s) the minimal period length, M P (u s) the companion matrix and a s 0 : : : a s d P (u s);1 the de ning coecients corresponding to the minimal recurrence relation of u modulo P s . Remark 1.18. As far as there is no confusion, we will simplify our notation by omitting unnecessary parameters, for instance, by cancelling the sign of the ideal P.For further properties of linear recurring sequences we refer to 24].Chapter 2
Dedekind-domains and modulesFor the discussions of the later chapters we will need some special properties of Dedekind-domains. In this chapter we state all the results we will use. The material of this and the 4th chapter is a generalization of 19].Throughout the chapter let R be a Dedekind-domain, and let P be a prime ideal of R. Suppose that R=P has N(P) elements, and N(P) < 1. Since R is a Dedekind-domain, P is maximal and R=P is a ( nite) eld (see e.g. 16]). Hence, we know that N(P) = l with some rational prime and an integer l 1 (see e.g.
24]). First we turn to the determination of N(P k ). For this we n e e d t h e f o l l o wing: Theorem 2.1. Let k 2 N . Then the additive groups of the rings R=P and P k;1 =P k are isomorphic. Proof. See e.g. 26]. Corollary 2.2. Let k 2 N . Then N(P k ) = N(P) k .Proof. By the isomorphism theorem of groups, we know that the additive groups of (R=P k )=(P k;1 =P k ) and R=P k;1 are isomorphic, thus