Dynamic passage name? (sugarcube)

So I'm trying to make it so a link goes to a specific passage. The player is on passage 8 and they want to go to passage 9, but in this circumstance I need to write 9 in relation to the current passage.

So I tried using:

[[Up|passage()+1]]

and it sends me to passage 81 instead of 9.

I tried it with a minus code:

[[Down|passage()-1]]

and it worked fine (took me to passage 7), the same with divide and multiply but not plus.