1. Bezboruah, A., Shepherdson, J.C.: Gödel's second incompleteness theorem forQ. J. Symb. Logic41, 503–512 (1976)
2. Hájek, P.: Positive results on fragments of arithmetic
3. Hirschfeld, J., Wheeler, W.: Forcing, arithmetic, division rings (Lect. Notes Math. 454). Berlin, Heidelberg, New York: Springer 1975
4. Lessan, H.: Models of arithmetic. Ph.D. thesis, University of Manchester, 1978
5. McAloon, K.: Completeness theorems, incompleteness theorems and models of arithmetic. Trans. Am. Math. Soc.239, 253–277 (1978)