Maluszynski, Jan and Martin Wirsing, editors, Proceedings of the 3rd International Symposium on Programming Language Implementation and Logic Programming (Passau, Germany), pages 255-274. Springer­Verlag, LNCS 528 (August 1991).

• Ait-Kaci, Hassan and Andreas Podelski (1991) Ait-Kaci, Hassan and Andreas Podelski "Towards a meaning of LIFE"
• Appel, A. et al, (1991) Appel, A. et al, "Standard ML of New Jersey"
• Naish, Lee (1991) Naish, Lee "Adding equations to NU-Prolog"