severak
2.8.2019 10:24:21
This result is folklore, which is a technical term for a method of publication in category theory. It means that someone sketched it on the back of an envelope, mimeographed it (whatever that means) and showed it to three people in a seminar in Chicago in 1973, except that the only evidence that we have of these events is a comment that was overheard in another seminar at Columbia in 1976. Nevertheless, if some younger person is so presumptuous as to write out a proper proof and attempt to publish it, they will get shot down in flames.
(from http://math.andrej.com/2012/09/28/substitution-is-pullback/#comment-21991)
— Paul Taylor