I am wondering what is the etiquette of publishing a "folklore" result? 


Though special cases of the result are well-known, the proof is not readily available in any reference text or paper I've seen. I will include it in the background of my thesis, and I could stick it onto another paper which I am working on (in which I use the folklore result). However, the paper I am working on is in a very niche area, whereas the proof of this result is useful to the bulk of researchers in my field. 


My options are:


* Include it in my current paper, which is in a niche subfield
* Put the result into a (very) short paper and submit it to some journal
* Post the proof on arXiv, and not submit it to a journal
* Post the theorem and proof on nLab


What are your thoughts? Are there any journals that accept this sort of "folklore" publication? Or am I better off just sticking the proof in my current paper or posting the proof on arXiv or nLab?



Etiquette of publishing folklore results
You ask for the "etiquette", which may differ from field to field. For the research community in computer science, the fate of one particular folk theorem has been documented in loving detail by David Harel in [On Folk Theorems](http://www.wisdom.weizmann.ac.il/~dharel/SCANNED.PAPERS/OnFolkTheorems.pdf) (1980).


One thing to note from this exposition, is that a characteristic of many folk theorems is that they are vague ("*While-programs compute everything*" is the particular example discussed by Harel), so they give rise to more than one version, and each version requires a seemingly different proof. Harel finds over 50 references to proofs of various incarnations of this folk theorem:



> 
> These proofs, which span fourty-four years, also span the complete
>  spectrum of recognized scientific literature: textbooks, monographs,
>  survey articles, journal papers, conference proceedings, newsletters,
>  theses, technical reports, lecture notes, letters to editors, and
>  self-referential folk tales.
> 
> 
> 


So I would conclude that for this field at least, publishing a proof of a folk theorem in whatever medium you find most convenient is "proper etiquette".


