1. Relativizations of the P=?NP question;Baker;SIAM J. Comput.,1975
2. S. Ben-David, S. Halevi, On the independence of P vs. NP, Technical Report # 699, Technion, 1991.
3. L. Beklemishev, Provability and reflection, Lecture Notes for ESSLLI’97, 1997.
4. Undecidability and incompleteness in classical mechanics;da Costa;Int. J. Theor. Phys.,1991
5. Consequences of an exotic formulation for P=NP;da Costa;Appl. Math. Comput.,2003