I am a Canadian professor at Korea University and would like to book a soft sleeper for myself and two of my colleagues. We would like to leave Beijing for Lhasa on July 20th, but we are flexible on the date of departure. I understand that we cannot book a return ticket, so do we book the train for Lhasa to Beijing when we arrive at the Lhasa train station? Of course we will also need Tibet permits. Can you give me guidance on how to get both the tickets and other necessary documents? Thank you for your assistance.