Euler systems and Special units

t is known that the order of the class group C_K of real abelian field K is essentially equal to the order of the quotient E_K/C_K of the units of K by the circular units of K, but the group structures of these two groups are usually very different. Motivated by the theory of circular distributions and that of the special units of Rubin. we introduce a filtration on E_K as a Galois module AND conjecture that the associated gradation is isomorphic, (as a Galois module) to C_K.. We use Euler systems to give evidence for this conjecture.