How to have several subjects when submitting an article to arXiv?
I would like to submit an article to arXiv and I have chosen a primary category so that the article is listed in that category. But I also would like to have another category in the list &quot;subjects&quot; when the paper appears on arXiv. For example, a paper is published on arXiv with &quot;Subjects: Analysis of PDEs (math.AP); bla bla bla&quot;. I am wondering how to add &quot;bla bla bla&quot;. Should it be done while doing cross-list?

Yes, the additional categories you see for an arXiv paper comes from specifying them in the cross-list. This can be done while submitting the paper. This help page provides further details.

If so, does the paper also appear in the second category mentioned? I do not wish to have the paper in several categories.

The paper will be announced to all the categories it is listed in, i.e., the primary category as well as the cross-listed categories. This is mentioned in the arXiv moderation page (emphasis mine):

arXiv moderation may result in the reclassification or removal of a submission. Reclassification by our moderators helps make sure that submissions are posted to the most appropriate archive. Cross-lists may be added to other related archives, or they may be removed by moderators when the classification is deemed inappropriate. A submission that is cross-listed to a category will still be announced in the mailings to that category.

However, it is possible to distinguish between primary and cross-listed categories when looking for a paper. In &quot;Advanced Search&quot;, it is possible to specify if papers cross-listed in the category being searched should be included in the results.
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