 Temporal-epistemic approaches have been briefly mentioned in this text.  Indeed, many logical systems have been used to describe the way in which the knowledge of agents changes over time. The proposals include not only interpreted systems (IS; Fagin et al. 1995) but also epistemic-temporal logic (ETL; Parikh &amp; Ramanujam 2003), logics of  agency  (e.g., see to it that logic,  STIT;  Belnap, Perloff, &amp; Xu 2001) and the DEL approach mentioned before  (section 2.8).  In all of them, an important point of discussion is the interaction between the temporal and epistemic modalities.