1. One hundred and two problems in mathematical logic;Friedman, Harvey;J. Symbolic Logic,1975
2. Recursiveness in 𝑃¹₁ paths through \cal𝑂;Friedman, Harvey;Proc. Amer. Math. Soc.,1976
3. Goncharov, S. S., Harizanov, V. S., Knight, J. and Shore, R. A., Π₁¹ relations and paths through 𝒪, in preparation.
4. Recursiveness of initial segments of Kleene’s 𝑂;Jockusch, Carl G., Jr.;Fund. Math.,1975
5. Π⁰₁ classes and degrees of theories;Jockusch, Carl G., Jr.;Trans. Amer. Math. Soc.,1972