Categories for the Working Mathematician

This text looks at the concepts of category, functor, natural transformation, and duality - and then adjoint functors - which provide a description of universal... » 

This text looks at the concepts of category, functor, natural transformation, and duality - and then adjoint functors - which provide a description of universal constructions, an analysis of the representations of functors by sets of morphisms, and a means of manipulating direct and inverse limits. «