And now something completely different

[timelets]

From Propp, Vladimir. Morphology of the Folktale. 1927. Trans., Laurence Scott. 2nd ed. Austin: University of Texas Press, 1968.

The Functions of the Dramatis Personae (in a true oral folk tale).

Theorems:

1. The functions of characters serve as stable, constant elements in a tale, independent of how and by whom they are fulfilled.
2. The number of functions known to the fairy tale is limited.
3. The sequence of functions is always identical.
4. All fairy tales are of one type in regard to their structure.
http://www-personal.umich.edu/~esrabkin/Propp.htm

It should be possible to express the structure of a true oral folk tale in terms of Category Theory. Per Theorem 4, a distinct structure is a category.

upd. Probably related from "Why Don't Students Like School?"