Dear Sirs: A typo has occurred in the original post, Correction: Define(Pi(H(d))) by recursion: For every ordinal d Pi(H(d))=H(d)for i=0 Pi(H(d))=P(Pi-1(H(d))) for any successor ordinal i Pi(H(d))=Union(j<i) Pj(H(d)) for any limit ordinal i were "P" stands for "power set". Best Regards Zuhair