It is said that it's possible to write anything in these halls. Jet is trying to prove them wrong.
"Right, but what if it includes racial slurs?"
The weary space-librarian rubbed its robo-temples. "Yes, one may write racial slurs in these halls. Many have."
But you don't, so you're unaware of the horrible history of oppression behind it, and hence allow this horrible transgression to pass. And doesn't that make you just as bad as Jet?
(I, the humble transcriber, have a g-word pass, so don't worry about me.)
"Huh, I could."
"Any other queries?" said the space-librarian.
Jet thought for a moment. "Right, what's the worst thing that I could write.... hm, how about a description of how the library shouldn't have everything written in it?"
"You may, and many have. They are stored in F293D120A1, if you are interested in prior work."
"Not really," said Jet, "I'm just being edgy. Hm, what about nonsense?"
"Section D022S191."
"What about true things?"
"Section L1929A922."
"Wait, is every true thing in section L1929A922?"
"Not every true thing," said the librarian, "but any true thing. Why would you expect there to be every true thing? This isn't a library of Babel; that's the one next dimension."
"Just wondering if, like, the thing that unfolds into every true thing has been written here. It's not like it's impossible to write in here, right?"
"It is possible to write in here. Indeed, it already has been. It merely unfolds into every true thing. It has not yet finished unfolding," said the librarian.
"Really thought I had you there. How about the thing that when written stops the library from having everything be allowed to be written in it?"
"Such a thing may be written, though it may not be read in these halls."
"But in that case, it doesn't stop things from being written, so the thing matching the description can't be written, so it's something that can't be written. Aha! I've beat you!"
The librarian looked sternly at Jet. "Come," the librarian set. Jet decided to follow. The librarian guided her through bookshelves, and then hallways, and then narrower hallways, and then hidden rooms, unlocked by pulling on books in bookshelves.
Finally, they came to a final room, deep within the halls. Inside the room was a podium. On the podium was a book.
"It usually takes visitors much less time to discover the paradox of the library. Behold, in this book. The one thing that cannot be written, not even in this halls."
Jet looked at the book, and looked again. It had one page, one sentence. She turned it over, but there was nothing else. Was that really it?
"I don't get it," said Jet. "All it says is 'a good punchline for this thread'."
Jet picked up the pencil and spun it round. "Bet," she said, and wrote the word "gorblax" inside those hallowed halls. If you knew what the word "gorblax" meant, you would be trying to cancel Jet simply for having it be inside quotes.