(en) Gaisi Takeuti, Proof Theory : Second Edition, Dover Publications, , 512 p. (ISBN9780486320670, lire en ligne), p. 386.
Maruti Ram Murty et Brandon Fodden, Hilbert's Tenth Problem : An Introduction to Logic, Number Theory, and Computability, American Mathematical Society, , 237 p. (ISBN9781470443993, lire en ligne), p. 119.