Fixed points for the jump operator (Q694226)

The major result in the paper under review is that there is a countable admissible set \(A\) so that \(J(A)\) is \(\Sigma\)-bi-embedabble with \(A\), where \(J(A)=HF(\text{Dom}(A),U)\) and \(U\) is a universal \(\Sigma\)-predicate on \(A\).