A：I’d like to join the library. We’re new to the district you see.

B：Certainly. Well all we need is some sort of identification with your name and address on it.

A：Oh dear. We just moved, you see, and everything has my old address.

B：A driving licence, perhaps?

A：No, I don’t drive.

B：What about your bank book?

A：That’s just the same. Oh dear, and I did want to get some books out this weekend. We’re going on holiday to relax after the move, you see, and I wanted to take something with me to read.

B：Well, I’m sorry, but we can’t possibly issue tickets without some form of identification. What about your passport?

A：What? Oh yes, how silly of me. I’ve just got a new one and it does have our new address. I’ve just been to book our tickets so I have it on me. Just a minute. Here you are.

I’ve just been to book，这里的have been后面为什么直接跟动词不定式to book?