I often will see the word "folklore" used in papers on category theory, e.g. in Barr's paper on Isbell Duality, he states a result, which he proves, is "folkloric", on page 512:
The following folkloric result goes back, in dual form in degree zero, to the fact that the diagonal chain complex associated to a double simplicial object is homotopic to its total complex
At first, I assumed it meant a result which everyone took as being true but no proof could be found in the publications (but not because a proof was't found). The term folklore makes me think it was a result found in the early days of research in category theory, 1950s-70s. It also has a disparaging tone to it, implying it might be untrue. But, it is true that "abstract nonsense" theorists are a self-disparaging bunch.
Could someone give me a good example of a result which has a folkloric feel to it?