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The category actually does not exist


It would be better to clearly define Hask, and either fix it to be a category, or admit it is not a category with a clear explanation of what is broken and what can be saved. (Formalize fast-and-loose reasoning.)

Looks like some of the information in the table is wrong. u2 _ = () is of type Empty -> (), not Empty -> a. As it stands, we don't have a real failure condition for the terminal object and arrow if you accept undefined :: Empty.