* If the duplicateness is discovered shortly after the question is posted, the solution is to **close as duplicate**.

    * Then the prospective voters will see the duplicate banner and are expected to go vote on the master question (or both).

* If the fact is discovered after both posts have coexisted for quite some time and accumulated a hefty sum of votes, the ideal solution is  [**merging**][1].

    * The catch here is such posts are often not _exact_ duplicates but rather "closely related", or have different focuses.
        * For the purpose of the site's M.O., this means that answers for one will not fit if moved to the other verbatim.
        * Of course, they can be edited to fit, but drastically changing a post's meaning would be appropriating its votes (because people voted on a different post that what you would make it into).
        * So, in these cases, the "least evil" solution seems to be **just prominently link them to one another.**


  [1]: https://meta.stackexchange.com/questions/158066/what-are-merged-questions