1. [1] Byrd, M., "Eventual permanence", Notre Dame Journal of Formal Logic, vol. 21 (1980), pp. 591--601.
2. [3] Rescher, N., and A. Urquhart, Temporal Logic, vol. 3 of Library of Exact Philosophy, Springer-Verlag, New York, 1971.
3. [4] Segerberg, K., An Essay in Classical Modal Logic. Vols. 1, 2, 3, vol. 13 of Filosofiska Studier, Filosofiska Föreningen och Filosofiska Institutionen vid Uppsala Universitet, Uppsala, 1971.
4. [2] Humberstone, L., "Weaker-to-stronger translational embeddings in modal logic", pp. 279--97 in Advances in Modal Logic, Vol. 6, edited by G. Governatori, I. M. Hodkinson, and Y. Venema, College Publications, London, 2006.