1. Elcock, E. W., Foster, J. M., Gray, P. M. D., McGregor, J. J., Murray, A. M.: ABSET, a programming language based on sets; motivation and examples. In : Machine Intelligence 6, 467–492 ( Meltzer, B., Michie, D., Hrsg.). Edinburgh: Edinburgh University Press 1971.
2. Fikes, R. E.: REF-ARF: a system for solving problems stated as procedures. Artificial Intelligence 1, 27–120 (1970).
3. Foster, J. M., Elcock, E. W.: ABSYS 1: an incremental compiler for assertions; an introduction. In: Machine Intelligence 4, 423–429 ( Meltzer, B., Michie, D., Hrsg.). Edinburgh Edinburgh University Press 1969.
4. Nevins, A. J.: A programming language with automatic goal generation and selection. J. Ass. Comput. Mach. 17, 216–230 (1970).
5. Robinson, J. A.: Mechanizing higher-order logic. In: Machine Intelligence 4, 151–170 ( Meltzer, B., Michie, D., Hrsg.). Edinburgh: Edinburgh University Press 1969.