finite extensions of Dedekind domains are Dedekind
Theorem.
Let be a Dedekind domain with field of fractions
. If is a finite extension
of fields and is the integral closure
of in , then is also a Dedekind domain.
For example, a number field is a finite extension of and its ring of integers is denoted by . Although such rings can fail to be unique factorization domains
, the above theorem shows that they are always Dedekind domains and therefore unique factorization of ideals (http://planetmath.org/IdealDecompositionInDedekindDomain) is satisfied.