Adding something to a book from an unpublished paper As many of the people that I am spamming in real life might at this point know, I am turning my coend note into a book.
I would like to add a few pages taken from a (still) unpublished paper of mine (et al.), but I don't know exactly what is the policy here: considering that


*

*the material I want to add is not exactly original; it is considered folklore or at maximum it is just an alternative proof of a known fact, or it is just recomposing a puzzle of pieces scattered in the literature.

*my coauthor agrees to see that section turned into a chapter of my book.

*it is not clear to me/us whether, should I decide to take this path, this would compromise the possibility for the paper to be published because it contains non-inedited material.

*the paper has been submitted, has been rejected, and will probably be resubmitted as soon as we edit it accordingly to the referee comments. It will probably be at the same time I submit the book to the publishing house.

*the book will not suffer from me not adding these 4-5 pages; only, I believe that those two particular proofs are useful, in-topic, and particularly aesthetically clean.

*I'd be inclined to see who comes first, and add "the present section already appears in [X, §y]" for suitable choices of $X\in \{journal,book\}$ and $y\in \sum_{x : X} \{sections_x\}$.


Considering all this, what's better to do? How free am I? Is it something I can (and should) discuss with the editor? Is this usually something regulated by the contract I signed?
Thanks!
 A: If the overlapping material is being reproduced verbatim (or nearly so), then technically, if you assign the copyright to the book publisher first, then you have to obtain the permission of the book publisher to include it in the paper (or vice versa, if you assign the copyright to the journal first). In practice, I would expect most publishers to be reasonable, but in principle, it isn't guaranteed that the publisher will grant this permission, so to be on the safe side, you may want to clarify this issue ahead of time.
Some publishers will let you retain copyright, or at least some rights, over your work. This is the best solution if you can negotiate it. (In fact, it's a good thing in general, even when you don't have plans to publish the material in two different places.)  Especially if it's just one chapter of a book, I would be optimistic that the book publisher will let you retain copyright over it.
If the material is conceptually the same but you're going to substantially rewrite it so that there are no long passages of text that are exactly the same in both works, then you shouldn't need to worry about copyright.  But I'm guessing that this is not the case.
