How to Use a Result Already Under Review in Another Paper? This may apply to any mathematical scientists. I am working on a paper, which (as far as I can tell) needs a result that I obtained. The result needed is a part of another paper of mine that is already under review. If I would like to submit the new paper, but need to cite the old one, how do I best work this issue out?
There are a couple of ways.


Upload a pre-print of the paper under review to ArXiV. Then you can cite the ArXiV version. This is commonly done in many fields, but typically happens at the time of submission to the journal. Check if this is actually allowed after submission to the journal by your specific journal.
As a less preferrable variant, upload your paper to your webpage (or to Dropbox or an alternative service) under a non-public link. Cite your paper under review in the new paper with the note "under review" and the link under which the paper can be obtained.


Variant 2 is common in case ArXiV cannot be used for copyright reasons (some journals do not accept papers that have already been published in any form). Note that some journals allow to submit supplementary material - it makes sense to include a PDF of the paper with the result that you want to use then. The non-public paper link is not necessary in this case.