Epstein, R. L. (1979). Degrees of unsolvability: Structure and theory. Springer-Verlag.
Lua i Stíl Chicago (17ú heag.)Epstein, Richard L. Degrees of Unsolvability: Structure and Theory. Berlín: Springer-Verlag, 1979.
Lua MLA (9ú heag.)Epstein, Richard L. Degrees of Unsolvability: Structure and Theory. Springer-Verlag, 1979.
Rabhadh: Seans nach mbeach na luanna seo go hiomlán cruinn i ngach uile chás.