inform((_:search,type,'Taxi'))
user
Yes , I would like a taxi to the Town Centre . From the train station .
request((_:search,departure,?);(_:search,type,'Taxi'))
system
Where from the town centre do you need the taxi to pick you up ?
inform((_:search,type,'Taxi');(_:search,type,'Train'))
user
I 'm sorry , did I say Taxi ? I mean train .
system
Let 's start over .   Are you looking for a train ?
inform((_:search,departure,'cambridge');(_:search,type,'Train'))
user
Yes . I need it to depart from Cambridge .
system
Where would you like the train from cambridge to travel to ?
_:search type Taxi
_:search departure ?
_:search type Taxi
_:search type Train
_:search departure cambridge
_:search type Train