Q:

Duplicate on other SE site

It turns out that this question
What is tail recursion?
has an answer at 
https://stackoverflow.com/questions/33923/what-is-tail-recursion
It is not possible to vote for closing as exact duplicate, since this requires a SE.cs question ID.
How can I proceed in this case. Should I vote for delete-off topic? 

A:

The answer on Stackoverflow is very concrete. I think our site should provide a more abstract/general treatment. Linking back and forth is a good idea in any case.

A:

Similar questions on different sites
Different communities will often offer different perspectives on the same topic. This is why there is no feature to close a question as a duplicate of a question on another site.
Add comments to link the questions to each other if you think that the answers on one site would be interesting to visitors from the other site. Feel free to reuse content from answers from one site (with proper attribution, of course) if you think that content is good from the perspective of the other site — but again remember that a good answer will usually give a different treatment on different sites.
Identical questions (multiposting)
Multiposting is discouraged as a matter of policy. If you see the same question (by the same asker, in a short lapse of time) on two or more sites:

Leave a comment linking to the other version(s) of the question so that answerers don't waste their time repeating what's already been said on another site.
Flag the question on all but one site. Close as off-topic if the question is borderline. If the question is genuinely on-topic on multiple sites, favor the one where it has the best answers. Moderators will arrange to merge and migrate if it is useful.

It's ok to ask about the same core problem on different sites, but the question must be tailored to each site. If you do this, be sure to cross-link the questions; this is useful both so that answerers don't waste time repeating what's been said on another site, and because future visitors are likely to be interested by both questions.
About this specific question
If the question was just “what is tail recursion”, I'd point to Wikipedia. This question is more specific, it's asking about a particular context. I think it deserves an answer tailored to that context.

