1. H.Ait-Kaci: "Outline of a calculus of type subsumptions", Technical report MS-CIS-83-34, Dept of Computer and Information Science, The Moore School of Electrical Engineering, University of Pennsylvania, August 1983.
2. A.Albano, L.Cardelli, R.Orsini: "Galileo: a strongly typed, interactive conceptual language", Bell Labs Technical Memorandum TM 83-11271-2.
3. G.Attardi, M.Simi: "Semantics of inheritance and attributions in the description system Omega", M.I.T. A.I. Memo 642, August 81.
4. O. Dahl, K. Nygaard: "Simula, an Algol-based simulation language", Comm. ACM, Vol 9, pp. 671–678, 1966.
5. P.Deutsch: "An efficient implementation of Smalltalk-80", Proc. Popl 84.