(Edited) I found that these four question are very similar: (One) (Two) (Three) (Four), and are abstract duplicates in my opinion.
However each question is "slightly" different then the next, perhaps adding in the word "elementary" or specifying a specific case of the more general formula. I think there needs to be some way to merge these questions as reader of any one would be equally interested by any of the answers contained in the others.
The current system, as outlined here, https://meta.math.stackexchange.com/questions/1756/coping-with-abstract-duplicate-questions suggest doing something along the lines of
Rewrite a more general question which encompasses all the others, flag all the other posts to be closed, and then repost all the answers on the new question as community wiki.
This feels like fixing a hole in a wall with duct tape. It is not pretty, and is not a long term solution.
Using the above method is very time consuming, which makes users less likely to do it. Also, the decision would come down to a user and the moderator, as opposed to a group of users. (Example: Voting to close/open) For this particular case, I am not 100% sure if it should be done, and would like to see that at least a few other users agree with me.
Main Point: I think there needs to be some mechanism to merge questions. I know that closing questions is suppose to fill this purpose, but it often fails to do so. Perhaps the ability to vote to merge should require more reputation, or after 5 votes it additionally must be ok-ed by a moderator. (as it is suppose to be used rarely) I understand there are ways to work around the current system, but none of these are satisfactory.