1. Barendregt, H. P. 1971 Some extensional term models for combinatory logics and λ-calculi, Dissertation, University of Utrecht.
2. 1977 The type free lambda calculus, in Handbook of Mathematical Logic, 1091–1132.
3. Barwise, J. and Schlipf, J. 1975 On recursively saturated models of arithmetic, in Model Theory and Algebra, Lecture Notes in Maths., 498, 42–55.
4. Principles of continuous choice and continuity of functions in formal systems for constructive mathematics;Beeson;Ann. Math. Logic,1977
5. 1979 Extensionality and choice in constructive mathematics (to appear). Continuity in intuitionistic set theories (this volume).