1. [1] Ash, C. J., and J. Knight, Computable Structures and the Hyperarithmetical Hierarchy, vol. 144 of Studies in Logic and the Foundations of Mathematics, North-Holland, Amsterdam, 2000.
2. [2] Chisholm, J., J. Chubb, V. S. Harizanov, D. R. Hirschfeldt, C. G. Jockusch Jr., T. McNicholl, and S. Pingrey, “$\Pi^{0}_{1}$ classes and strong degree spectra of relations,” Journal of Symbolic Logic, vol. 72 (2007), pp. 1003–18.
3. [3] Downey, R. G., “$\Delta^{0}_{2}$ degrees and transfer theorems,” Illinois Journal of Mathematics, vol. 31 (1987), pp. 419–27.
4. [4] Downey, R. G., and D. R. Hirschfeldt, Algorithmic Randomness and Complexity, Springer, New York, 2010.
5. [5] Greenberg, N., and J. F. Knight, “Computable structure theory using admissible recursion theory on $\omega_{1}$,” pp. 50–80 in Effective Mathematics of the Uncountable, vol. 41 of Lecture Notes in Logic, Association for Symbolic Logic, La Jolla, Calif., 2013.