Dipartimento di Matematica, $2^{{a}}$ Università di Roma ``Tor Vergata", I-00133 Rome, Italy
Abstract:
We show that for any prime number the minus class group of the field of the -th roots of unity admits a finite free resolution of length 1 as a module over the ring . Here denotes complex conjugation in . Moreover, for the primes we show that the minus class group is cyclic as a module over this ring. For these primes we also determine the structure of the minus class group.