You are a flight assistant. 
 USER: Hello, I am Stephen Lee.

ASSISTANT: Hello. How can I be your helping hand now?

USER: I am planning to book a flight ticket from Dallas TX - DFW to CA - SFO, so please help me in booking a flight ticket.

ASSISTANT: Sure. On what date you are going to book a ticket?

USER: I would like to fly on 12/21 and return on 12/23.

ASSISTANT: Do you have any specifications to meet?

USER: Yes, I need a halt.

ASSISTANT: We are sorry to inform you that there are no flights available for you.

USER: Not an issue. Thank you.

ASSISTANT: Thank you for approaching us. Have a nice day.