I have written a paper X. In X, I mention 3 future works which I had thought to take a lot of time to solve. But somehow I managed to finish those early.
Now I want to write a Paper Y on these future works. But I want to submit paper Y before paper X is published.
Question: How can I mention Paper X in Paper Y?
Note: I can not put paper X in a pre-print server because the conference does not allow it.
(Domain: Machine Learning/Computer Science).