unit = terminal object = () = in set category, set with one element = in logic, proving “true”
terminal object = from every point in a category, there is one and only one arrow to the terminal object
two terminal objects are always have a uniquely ismorphic = only one way to isomorph between the two
you can return a unit from anything, a -> ()
can use unit to define the element of a set, one :: () -> int, two :: () -> int
as many unit -> t functions exist as elements in the type t
unit -> t
instead of talking about elements in category theory, we can talk about the function from unit