A preliminary to the sequel : 8 (8+?) ways to define natural transformations ! Feel free to comment/get in touch 1 - an exemple using injections in Set 2 - an exemple in programming with the category "Hask" of types and functions 3 - what happens when the domain is a discrete category 4 - what happens when the codomain is a discrete category 5 - what happens when the codomain is a poset 6 - You already know what happens when the domain is discrete and the codomain is a poset 7 - what's a "Natural Isomorphism"