1. K.R. Apt and M.H. van Emden. Contributions to the Theory of Logic Programming. Journal of the ACM, Vol. 29, No. 3, pp. 841–862, 1982.
2. P.G. Bosco and E. Giovannetti. IDEAL: An Ideal Deductive Applicative Language. In Proc. IEEE Internat. Symposium on Logic Programming, pp. 89–94, Salt Lake City, 1986.
3. R. Barbuti and R. Giacobazzi. A Bottom-Up Polymorphic Type Inference in Logic Programming. Technical Report 27/89, Dip. di Informatica, Università di Pisa, 1989.
4. M.H.M. Cheng, M.H. van Emden, and B.E. Richards. On Warren's Method for Functional Programming in Logic. Report LP-12 DCS-122-IR, Univ. of Victoria, 1989.
5. L. Cardelli and P. Wegner. On Understanding Types, Data Abstraction, and Polymorphism. acm computing surveys, Vol. 17, No. 4, pp. 471–523, 1985.