1. Baader, F., ?The theory of idempotent semigroups is of unification type zero?, J. Automated Reasoning 2, 283?286 (1986).
2. Baader, F., personal communication, 1989.
3. Book, R. and Siekmann, J., ?On unification: equational theories are not bounded?, J. Symbolic Computation 2, 317?324 (1986).
4. Bürckert, H.-J., Herold, A. and Schmidt-Schauß, M., ?On equational theories, unification, and decidability?, Proc. 2nd Conference on Rewriting Techniques and Applications, LNCS 256, Springer, 1987, pp. 240?250. Also Kirchner, C. (Ed.), J. Symbolic Computation, Special Issue on Unification, 1989.
5. Kirchner, C. (Ed.), J. Symbolic Computation, Special Issue on Unification, 1989.