We present an application prototype of dynamic knowledge representation programmed in LUPS (a language for updating logic programs). This is a case study to model intelligent agents in logic and we use a calendar example in order to explain their features, such as non-monotonic reasoning in scheduling appointments, making belief revision, and negotiating proposals. We argue that LUPS is an excellent language to model an intelligent calendar agent by means of a practical prototype. Several other challenges are suggested as well, so as to achieve a more powerful and useful multi agent system. KEY WORDS agent, calendar, lups, dynamic knowledge, non-monotonic reasoning