1. Degrees of unsolvability of constructible sets of integers;Boolos;J. Symb. Logic,1968
2. A recursion-theoretic characterization of the ramified analytical hierarchy;Boyd;Trans. Am. Math. Soc.,1969
3. An annotated bibliography for the structure of the degrees below 0′ with special reference to that of the recursively enumerable degrees;Cooper;Recursive Function Theory Newsletter,1974
4. An introduction to the fine structure of the constructible hierarchy;Devlin,1974
5. A note on the hyperarithmetic hierarchy;Enderton;J. Symb. Logic,1970