1. Y. Auffray. Résolution modale et logique des chemins. PhD thesis, Université de Caen, France, 1989.
2. Y. Auffray and P. Enjalbert. Modal theorem proving: An equational viewpoint In Int. Joint Conf. on AI, 1989.
3. Y Auffray and P. Enjalbert. Modal theorem proving: An equational viewpoint. Journal of Logic and Computation, 1990.
4. L. Catach. Normal multi-modal logics. In Proc. Nat. Conf. on AI(AAAI'88), pages 491–495, 1988.
5. L. Catach. Les logiques multi-modales. PhD thesis, Université Paris VI, France, 1989.