Browsing by Subject "model morphism"

We develop the theory of categories from foundations up. The thesis culminates in a theorem in which we assert that any concrete functor between categories of models of algebraic theories, where the codomain categories' alphabet does not contain relational information, has a left adjoint functor. This theorem is based on The General Adjoint Functor Theorem by Peter Freyd. The first chapter is about the set theoretic foundations of category theory. We present the needed ideas about recursion so that we may define what is meant by first order predicate logic. The first chapter ends in the exposition of the connection between the Grothendieck universes and the inaccessible cardinals. The second chapter starts our conversation about categories and functors between categories. We define properties of morphisms, subobjects, quotient objects and Cartesian closed categories. Furthermore, we talk about embedding and identification morphisms of concrete categories. Much of the third chapter is to show that the category of small categories is a Cartesian closed category. This leads us to talk about natural transformation and canonical constructions relating to functors. To define equivalences and their generalizations, adjoint functors, natural transformations are needed. The fourth chapter enlarges our knowledge about hom-functors and their adjacent functors, representable functors. The study of representable functors yields a profound lemma called Yoneda lemma. Yoneda lemma implies the fully faithfulness of Yoneda embedding. The fifth chapter concentrates to limit operations in a category, which leads us to talk about completeness. We find out how limit procedures are preserved in constructions and how they behave when functors pass them forward. The last chapter is about adjoint functors. The general and the special adjoint functor theorems, due to Peter Freyd, are proven. Using The General Adjoint Functor Theorem, we prove the existence of a left adjoint functor for all suitable forgetful functors among algebraic categories.