# When should posts be closed as duplicates?

One could answer " when they are the same" but what if a question is answered by combination of more than one old post?

So, let's say a question ask how to show a statement C from a statement A but previously two questions were asked " show statement B from statement A" and " show statement C from statement B". How would one close then?

Honestly I feel it should be closed but its unclear on what basis it should be closed. It seems so the criteria for its closure is in some sense beyond the SE system.

• Perhaps an example or two would be a good idea, Generally...well, every mathematical argument can be broken down into a combination of other arguments, so your notion of "duplicate" would cover a lot of ground.
– lulu
Aug 14 at 12:10
• Maybe we should cross this bridge when we come to it. Aug 14 at 12:15
• @GerryMyerson I suspect that this question is directly related to this answer, and my comments below that answer.
– Xander Henderson Mod
Aug 14 at 12:24
• Conclusion: If the set of duplicate forms a space having dimension $2$ or more , then the question can't be closed. ( two duplicate posts are independent if both can be proved independently). For an example consider the following question : Does there exist any function $f:\Bbb{R}\to\Bbb{R}$ which is continuous only on rational? $\\$ First duplicate : The set of continuity forms a $G_{\delta}$ set. $\\$ Second duplicate: $\Bbb{Q}$ is not a $G_{\delta}$ set. $\\$ This question can't be closed as both the duplicate target have independent proof. Am I right @XanderHenderson ? Aug 14 at 13:19
• ... If yes then it should be clearly mentioned in the EoQS page. Aug 14 at 13:23
• Hmm, I mean, if each fine point was mentioned, then the page would be very long. The goal should be to quickly convey the general idea. Exceptional issues can probably given their own threads (like here for instance) Aug 14 at 13:25