inform((_:search,day,'friday');(_:search,type,'Train'))
user
I need a train leaving on Friday .
request((_:search,departure,?);(_:search,destination,?);(_:search,type,'Train'))
system
Where are you departing from and what is your destination ?
inform((_:search,departure,'cambridge');(_:search,destination,'ely');(_:search,type,'Train'))
user
The train should depart from cambridge and should go to ely .
request((_:search,leave_at,?);(_:search,type,'Train'))
system
Is there a particular time you 'd like to leave ?
inform((_:search,arrive_by,'08:15');(_:search,day,'friday');(_:search,type,'Train'))
user
I would like to leave on Friday and should arrive by 08:15 .
system
Booking was successful , the total fee is 4.4 GBP payable at the station . 
 Reference number is : 57E550PF .
_:search day friday
_:search type Train
_:search day friday
_:search departure cambridge
_:search destination ely
_:search type Train
_:search departure cambridge
_:search destination ely
_:search leave_at ?
_:search arrive_by 08:15
_:search day friday
_:search type Train