1. N. D. Goodman, A theory of constructions equivalent to arithmetic, in: Intuitionism and Proof Theory, ed. A. Kino, J. Myhill, and R. E. Vesley (North-Holland, Amsterdam, 1970) 101–120.
2. N. D. Goodman, A simplification of combinatory logic, to appear in J. Symb. Log.
3. W. W. Tait, Functionals defined by transfinite recursion, J. Symb. Log., 30(1965) 155–174.