with some of the other TAC participants  Section   presents possible directions for future research and concludes

## 2. Tac

A TAC game instance pits   autonomous bidding agents against one another  Each TAC agent is a simulated travel agent with    clients  each of whom would like to travel from TAC
town to Boston and back again during a common day period Each client is characterized by a random set of preferences for the possible arrival and departure dates hotel rooms The Grand Hotel and Le Fleabag Inn and entertainment tickets symphony theater and baseball To obtain utility for a client an agent must construct a travel package for that client by purchasing airline tickets to and from TACtown and securing hotel reservations it is possible to obtain additional utility by providing entertainment tickets as well A TAC agent s score in a game instance is the difference between the sum of its clients utilities for the packages they receive and the agent s total expenditure TAC agents buy flights hotel rooms and entertainment tickets in different types of auctions  The TAC server running at the University of Michigan  maintains the markets and sends price quotes to the agents  The agents connect over the Internet and send bids to the server that update the markets accordingly and execute transactions EE
auctions of different types Flights (8 auctions):  There is a separate auction for each type of airline ticket  flights to Boston  inflights  on days      and flights from Boston  outflights  on days There is an unlimited supply of airline tickets and their ask price periodically increases or decreases randomly by from $   to $    In all cases tickets are priced between $
When the server receives a bid at or above the ask price the transaction and $
is cleared immediately at the ask price No resale of airline tickets is allowed Hotel Rooms (8):  There are two different types of hotel rooms   the Boston Grand Hotel BGH  and Le Fleabag Inn  LFI    each of which has     rooms available on days The rooms are sold in a th price ascending English auction meaning that for each of the types of hotel rooms the highest bidders get the rooms at the th highest price For example  if there are     bids for BGH on day    at $
bids at $
and any number of lower bids  the rooms are sold for $      to the     high bidders plus one of the $
bidders  earliest received bid   The ask price is the current   th highest bid Thus agents have no knowledge of for example the current highest bid New bids must be higher than the current ask price No bid withdrawal and no resale is allowed  Transactions only clear when the auction closes  To prevent agents from all waiting until the end of the game to bid on hotel rooms  hotel auctions can close after an unspecified period  roughly one minute  of inactivity   no new  bids received Entertainment Tickets (12):  Baseball  symphony  and theater tickets are each sold for in continuous double auctions  Here  agents can buy and sell tickets  with days transactions clearing immediately when one agent places a buy bid at a price at least as high as another agent s sell price Unlike the other auction types in which the