A reflective subcategory is a full subcategory such that objects and morphisms in have “reflections” and in . Every object in looks at its own reflection via a morphism and the reflection of an object is equipped with an isomorphism . A canonical example is the inclusion of the category of abelian groups into the category of groups, whose reflector is the operation of abelianization. A useful property of reflective subcategories is that the inclusion creates all limits of and has all colimits...