The cyclic subfield integer index
In this note we consider the index in the ring of integers of an abelian extension of a number field of the additive subgroup generated by integers which lie in subfields that are cyclic over . This index is finite, it only depends on the Galois group and the degree of , and we give an explicit combinatorial formula for it. When generalizing to more general Dedekind domains, a correction term can be needed if there is an inseparable extension of residue fields. We identify this correction term...