Sometimes it happens that a published paper refers to an unpublished paper for a result used.
In this case, if we want to check this result by ourselves, we need to access to this unpublished paper.
Question: What is the usual process for accessing to an unpublished paper?
Is it the duty of the author (citing it in his published paper) to send it to anyone requiring it?
Or is it the duty of the editor, or of the author of the unpublished paper?
What to do if we can not get it through these means?