1. Aanderaa, S., Cohen, D.E.: Modular machines I, II. In: [2], pp. 1–18, 19–28 (1980)
2. Adian, S.I., Boone, W.W., Higman, G. (eds.): Word Problems II: The Oxford Book. Studies in Logic and the Foundations of Mathematics, X + 578 p., North-Holland (1980)
3. Ambos-Spies, K., Kjos-Hanssen, B., Lempp, S., Slaman, T.A.: Comparing DNR and WWKL. J. Symbolic Logic 69, 1089–1104 (2004)
4. Barwise, J., Keisler, H.J., Kunen, K. (eds.): The Kleene Symposium. Studies in Logic and the Foundations of Mathematics, XX + 425 p., North-Holland (1980)
5. Basu, S.S., Simpson, S.G.: Mass problems and intuitionistic higher-order logic, 44 p., 12 August 2014.
http://arxiv.org/abs/1408.2763