From Polya fields to Polya groups: (I) Galoisian extensions

The Polya group of a number field K is the subgroup of the class group of K generated by the classes of the products of the maximal ideals with same norm. A Polya field is a number field whose Polya group is trivial. Our purpose is to start with known assertions about Polya fields to find results concerning Polya groups. This first paper inspired by Zantema's results focuses on the Polya group of the compositum of two galoisian extensions of Q.