A beginner learning about parametricity and the relationship between Functorial composition and Functor identity brought up a good point to me: the documentation for Bifunctor[1] and Profunctor[2] both explain the relationship between parametricity and their laws, particularly what constitutes a minimum "burden" of proof. I don't have an exact wording yet, but I think it would be a good idea to update the Functor documentation accordingly. A separate point of issue: The line "The instances of Functor for lists, Maybe and IO satisfy these laws." This statement is redundant at best when you consider that Haskellers aim for instances of Functor to be lawful. At worst it could leave beginners confused and with more questions. I could imagine someone interpreting this statement as saying there might exist some unlawful instances. I think this line should just be removed. Let me know what you think. Thanks