1. Recursive functions and regressive isols;Barback, J.;Math. Scand.,1964
2. A note on regressive isols;Barback, Joseph;Notre Dame J. Formal Logic,1966
3. Two notes on regressive isols;Barback, Joseph;Pacific J. Math.,1966
4. Double series of isols;Barback, Joseph;Canadian J. Math.,1967
5. Regressive upper bounds;Barback, Joseph;Rend. Sem. Mat. Univ. Padova,1967