1. Floyd, R. W. [1967], Assigning meanings to programs, Proc. Symp. in Applied Mathematics, vol. 19 (J. T. Schwartz, ed.), American Mathematical Society, Providence, RI, pp. 19–32.
2. Gentzen, G. [1938], New version of the consistency proof for elementary number theory, The collected papers of Gerhart Gentzen (M. E. Szabo, ed.), North Holland, Amsterdam (1969), pp. 252–286.
3. Gorn, S. [Sept. 1965], Explicit definitions and linguistic dominoes, Proc. Conf. on Systems and Computer Science, London, Ontario, pp. 77–115.
4. Iturriaga, R. [May 1967], Contributions to mechanical mathematics, Ph.D. thesis, Carnegie-Mellon Univ., Pittsburgh, PA.
5. Knuth, D. E. and P. B. Bendix [1969], Simple word problems in universal algebras, Computational Problems in Universal Algebras (J. Leech, ed.), Pergamon Press, Oxford, pp. 263–297.