i need to book a train friday to london .
{'service': 'train', 'act': 'request', 'slot_name': 'depart', 'value': '?'} {'service': 'train', 'act': 'request', 'slot_name': 'arrive', 'value': '?'} {'service': 'train', 'act': 'request', 'slot_name': 'leave', 'value': '?'}
first i need your departure and the times you want to leave or arrive .