"We will not have books, right?"
Translation:לא יהיה לנו ספרים, נכון?
Yes, it's a mistake - but often, this is how people would say it. My guess is that people do it as an extension of present tense "אין לנו ספרים" where the אין doesn't change depending on the noun.
Well ain isn't connected the the books I do not believe. It is stating that there is an absence to us. Books clarifies what that absence is. Could be wrong though.
Anyways, since all correct answers should be accepted, shouldn't using yiyu be accepted? Because it wasn't.
I meant that לא יהיו לנו ספרים is the correct way. לא יהיה לנו ספרים is the mistake.