A TAC Travel agent is a simulated travel agent whose task is to organize itineraries for clients who wish to travel from TACTown to Boston and back again. Travel goods, such as airline tickets and hotel reservations, are complementary, while tickets to entertainment events, such as the Boston Red Sox and the Boston Symphony Orchestra, are substitutable. The agent's objective is to procure those goods that best satisfy its clients' preferences as inexpensively as possible, by trading in ascending call markets, continuous double auctions, and dynamic posted-pricing environments, simultaneously.